I was under the impression that some grunts were aware of Ghetsis's true intentions. From a translation of the Japanese dialogue:
Grunt: W-What's this...?!
Isn't that Lord Ghetsis...? The one who was giving that speech to fool everybody?!
I think either they had alternate motives themselves, or just needed money/joined for fun judging by the sheer amount of times they hammily shout "PLASMA!"
The Sages were definitely at least somewhat aware of Ghetsis's motives- they mistakenly refer to him as "Lord" Ghetsis a few times, followed by him reminding them that he is equal to them.