It seems as though every bit of data(save games,data files, etc.) for the games from Onlive are stored on their own servers in a cloud-like system, so trainer applications on you pc would not be able to effect the game(s) without direct cooperation from Onlive. in short, no. or rather, not right now anyway.
originally posted by OnLive: Gaming's Biggest Gamble by Joe Sinicki:
Cheat Happens Co-Founder and Business Manager Chris O’Rorke is hopeful that the site can find a way to use the OnLive service to their advantage. “Since the OnLive service uses PCs and PC games to power their gaming cloud, it’s entirely feasible that our trainers and software would function with no problem,” O’Rorke said . “The key would be getting OnLive to allow them to be run along with the game.” That’s the key though, would the service allow the trainers and mods from Cheat happens to run on their servers? O’Rorke is hopeful. “ Since our trainers are completely legal and pose no threat to multiplayer games, it’s possible that OnLive would allow these types of mods to be run, but at this point we have not attempted to contact them about this type of integration. Were we able to integrate our trainers into their service, it would give us access to an entirely new group of users that previously could not benefit from our software, such as MAC users, iPad users, etc.”