Well it's like Stan says, he's all about the money. He doesn't care so much where it's coming
from, just so long as it's coming
in.
Stan
motivated at least two of the charges brought against Guybrush during the trial, which he did to try and make money. He was also merchandising the Guybrush paraphernalia to the same end during the trial.
After the trial Stan starts
selling the LeChuck/Voodoo Lady stuff to try and make a quick buck on that front.
He's allowed to hold a grudge against things like Guybrush nailing him inside that coffin or scamming his insurance company. It doesn't mean Guybrush isn't allowed to be sore about Stan getting the best of him (such as when he sells him the Sea Monkey). That's the dynamic that they share. They both essentially just take turns screwing each other over.
But I doubt Stan would really care until it comes into light how he could make money off the situation.