Not a bad idea. I think it could be a passive ability so as to not force the player to care - since lets face it, missions that most people farm for exp are those where you put tanks on AUTO ON, and just do other stuff.
While yes farming Ocica is a good way as well, that map requires babysitting due to the amount of crap, enemies and HT enemy commander, if you wanna avoid losses (which still happens to me occasionally if a really bad enemy spawn hits).
Personally I think it would be best to increase the tank EXp on a global scale. For dupes, you get +30% exp.
I think every tank should start at 20% since day 1, or get buffed to 20% after you hit Commander lvl 45-50, while feeding dupes to a tank would up it to 50% (so still 30% for feeding dupes to your tank, but with extra 20% as a base to start with, either from a certain Commander level or straight from the get go).