Well, yes and no. How did you become very wealthy in the first place without being the government? If you're wealthy, you presumably own the land and have tenants to farm it for you (and some suitably armoured thugs to enforce your labour contracts), that's what wealth is. And at that point you are the government, for all practical purposes, even though it's not a formal "feudal" system by any means.

If you're asking, could a stranger with a lot of gold come in and bribe his way to the top, the answer is probably no. Why take a bribe to fight for some stranger when you can just as easily bash him over the head and take all the gold? As for bribing the peasants to rise up, if they had any hope of victory they'd likely have done so anyway. It's not motivation they need, it's weapons and training.

Now, if your wealth was in the form of weapons, armour, and loyal fighting men, that's something else again; but then we don't usually call the method "subversion".