Although I do consider it a minor exploit, sometimes I like to research Mass Driver Theory really early and trade or sell it to all of the other races - but make sure not to give them Space Weapons. Pretty soon all of the other races are developing mass driver weapons, then I can develop one type of armor that will work against everyone.
Thats not an exploit, thats just good strategy and mastery of the game. At some point, everyone just learns how to succeed, what works, and what doesnt, and how the AI thinks about things. If thats an exploit, then every succesful strategy in the game is based on some "exploit" or another.
Seeding technology is just good planning and dastardly thinking. I seed Trade as quickly as possible to every race to reduce diplomatic hostility and gain income with minimal effort(construction) on my part. I build influence bases right next to a race's homeworld, then gift them to another race to keep relations strained and prevent alliances. Sneaky, yes, exploit, no. Advanced understanding of the game is not an exploit.
I think the definition of exploit is much more narrowly defined as something being gamebreaking and not in the spirit of your races capabilities, and completely unintended by the developers.