I apologies before hand for the grammar:
I would say that to have slave pits when you have chosen the good alignment is hypocritical.
First of, let's look at what the game say is good an evil. After you have played the game a few times it gives you a pretty thorough explanation of what it (the game) means by good and evil. Namely the moral choices that pop up now and then. Not only is the, IMO, overlaying theme that the good choices are what humans would call "good". They actually have a few about slaves. I do not remember the wording exactly but the picture is of a farm (IIRC) and you get the evil options of "slaves, can't have enough of them"
and get a production bonus. Whereas the good option is to not have any slaves and you get no production bonus.
So saying that the meaning of the word good is different depending on the perspective is a bit redundant since the game gives you a clear definition of what it means about good and evil. And it is in the game that you choose which alignment you should take, you don't call up Lord Kona and ask if he could change the meaning of the word so that you can get the Mind Control center and Neutral Learning Centers at the same time (but it would be sweet

).
I would however like to argue for the point that what we see as good and evil can be universal.
Good societies use slavery as well- it's called prison labor.
Sure I believe that most countries that has prisons make the most prisoners work in some fashion. However if the society is good there would be no where near the amont of prisoners as there would be a non-prison workforce. Without profiling, and the focus on rehabilitating rather then punish there would be fewer and shorter prison terms.
To take a real world example. According to http://www.kcl.ac.uk/depsta/rel/icps/world-prison-population-list-2005.pdf USA has the highest incarceration rate, 714 persons out of every 100,000. Even though that is our worlds highest it equals to a very small workforce. So I believe that a "slave-prisoner" economy would not be very effective. I also believe that a prison work force doesn't have the same work moral, creativity or efficiency then a content "normal" worker. Sure if you punish them severely enough they would probably not drag their feet, but then we would be back into evil territory.
Hitler never owned a slave. Was he a good person then?
A bit OT but Hitler enslaved millions of people in camps and made them work to death. And even if he hadn't endorsed it there are more benchmarks then slavery for evilness
What point? That slavery is inherently bad...to a Drengin?...for whom it has been an ingrained norm underpinning their cultural infrastructure for over 100,000 years?
An interesting point! However we have had it similar on earth. Slavery has been a round for many thousand years. And even though slavery has been a part of one of the bigger religions, Christianity, for thousand of years (for example Leviticus 25:44-46 NLT) now many (a majority?) of humans believe that slavery is wrong. We even had our own versions the Drengin arenas where gladiators fought to death to the amusement of others. And even then we still believe that slavery is bad now.
But how can I argue that good and evil can be universal?
Because of empathy, or more specifically mirror neurons. Basically they are neurons that are active both when you do something and when you see someone else is doing something. Have a read at http://www.edge.org/3rd_culture/ramachandran/ramachandran_p1.html it's very interesting. The wiki article http://en.wikipedia.org/wiki/Mirror_neuron is perhaps easier to read, but then remember to be skeptical!

Anyhow, since they activate when other beings do things they give us the ability to learn from things other people do. And this is a very powerful tool for learning complex things. For example after I read Purges "Detailed Suicidal AAR for DA" (a very good read https://forums.galciv2.com/?forumid=350&aid=163571 ) I was able to go from Painful to win a Masochistic in the TA beta.
How does this correlate to empathy being universal? Well first of most of the bigger animals on earth have mirror neurons so this is in no means just a human thing. They make monkeys able to learn to use tools by watching each other. And they also make us squirm when we see something really horrible being done to someone else. For example seeing someone beeing stabbed makes the mirror neurons fire, mirroring the behavior/sensation of the stabbed person. And what I believe IMHO to be universal about this is that mirror neurons are crucial to make a species learn complex things.
So my definition of good would then be a very classic sentiment: Do to others what you want them to do unto you.
And evil would be the opposite: You get more stuff being a greedy bastard and don't caring how your actions hurt others.
Hence no good slave pitts.