It depends on the guy. Generally speaking I would expect if a guy is a purveyor of polyamory he's not going to mind being approached by a woman.
For me, one of the most liberating things about polyamory is that we get to make our own rules. As long as there is open and honest communication and agreement between all parties, then we can do whatever is comfortable.
Me: 48 - Married, straight, male
Shiela: My wife.
Suzanne: My FWB
Adam: Shiela's LDR