There are three main reasons to build Robots.
1 to do jobs that we cannot do.
2 to do jobs that we do not want to do.
3 to do jobs that we do not have enough people to do.
jobs that we cannot do.
work in a nuke core
work below a certain depth underground or underwater.
jobs we do not want to do
sweep the floor
cook
weed
jobs we do not have enough people to do
factories.
these three things are what most races would build their robots to do. meaning that they would or at least some of them would be able to take a lot more punishment than their living counter parts could.
Now this is an assumption on my part. But, if the Robots did rebel would they not use the toughest models to build themselves after. Sure in human(Iconian) form but modeled after the ones that could take the most punishment.
Your basic assumption is that sentient robots would be designed initially to do manual labor, or other "tough" jobs. That assumption makes little sense because nobody would put a $5,000,000 positronic brain in a robot that is going to sweep floors. A floor sweeping robot (which we already have BTW) just needs solid programming, not the ability to learn and eventually to think on its own. Same with a robot working in areas with lots of radiation, they need to be able to do the same task endlessly, or take certain commands from an outside human observer if there is a crisis, they do not need to be able to think on their own. As a matter of fact, who would want an intelligent robot to be left unsupervised in a nuclear reactor?
No, if sentience ever comes to robots it will be in ones designed to mimic humans (or their creators) in almost all ways. These will initially be the playthings of big corporations and the rich, much like the most human seeming robots are today. Yes, a "race" of robots might eventually be designed for specific jobs, so some will be quite tough, but they will also often be built for aesthetic appeal. They are sentient after all, so they might actually learn to appreciate beauty, or at least symmetry and pleasing geometric design.
Regardless, I doubt that any being that is sentient will ever exist that does not have a highly delicate "brain". Indeed, Sentient robots would probably actually be more vulnerable to brain damage from outside sources than humans, unless they put heavy protection around their brain. Did you know that computer parts in jet airplanes need radiation shielding because the natural protection from radiation at high altitudes is so much less and one tiny bit of radiation hitting a transistor in a CPU can permanently fark it the heck up, possibly leading to a crash and burn situation. This same problem can even happen on the surface of the earth though it is highly unlikely. Still corporations with extremely vital computer systems put in radiation shielding just to make sure. Imagine then a robot brain that is 1,000,000 times more sensitive than modern CPUs. Robots would need heavy radiation shielding just to survive on the surface of a normal planet, let alone a radioactive one.
So a radioactive planet would probably kill robots immediately, and shielding heavy enough to survive such radiation would make them large and ugly, which they probably would not enjoy. Similarly, because of their many delicate parts, survival in any other hostile environment would require just as much protection as a human would require, maybe more, it would just be designed differently. To put it in perspective, would you like to live the rest of your life in a spacesuit on an uncomfortable planet where one mistake will kill you? I didn't think so, so why would a sentient robot?
Short and sweet:
Radioactive world = Massive shielding at all times or instant death. Creating new life difficult because it is harder to shield a new brain while it is being built, and requires basically the same technology other races would use to survive on a radiated planet in the first place.
Aquatic world = Built like a submarine or instant death. Massive amounts of maintenance needed. Creating new life would require protective high-pressure domes, so creating new life requires the same technology other races would use to survive on an aquatic planet in the first place.
Heavy Gravity world = All delicate parts built with massive amounts of extra support, or instant death. Must be designed to sit low to the ground to avoid excess strain on body structure. Creating new life almost impossible without anti-gravity because of the sensitive nature of the process, so creating new life requires the same technology other races would use to survive on a high gravity planet in the first place.
Toxic world = Bulky anti-corrosion design required, or rapid death. Massive amounts of maintenance needed because anti-corrosion equipment will wear out. Creating new life will require a large enclosed space that is invulnerable to toxins, so creating new life requires the same technology other races would use to survive on a toxic planet in the first place.
Barren world = Likely insufficient metals, silicates, or other vital elements, to sustain life, slow death is inevitable without regular outside support. Creating new life is virtually impossible because of limited raw materials, so creating new life requires new technology different, but somewhat similar to what other races would use to survive on a barren planet in the first place.
So basically what it really comes down to is that even robots need new technology to survive hostile environments, they would not automatically be built to survive them, and it would not be any easier for them than for any other life form.
