One potential danger here is single friends seeing you/your partner on the app. In the ideal world they'd bring this to your attention and you'd be able to explain it away easily. In the real world it's absolutely how vicious rumors start.

unless you're already accustomed to jealousy management via some sort of ENM, it's probably unwise.

if his wife is pretending to be him this shouldn't be an issue.

Could easily result in her losing interest in him when she sees how coldly other women treats him. Emotions are fickle and an experience like that might change the way she sees him.