Yes, it would.
MFM is my biggest turn-on (after watching two women together).
I would have to be bigger than the other dude, by a little bit. If we were the same size, or close to it, it might cause some friction, but maybe a big turn-on somehow. Otherwise, if he's apparently bigger than me, I think jealously would ruin it for me (very, very few dudes would be bigger than me, especially in girth).
I wouldn't do an MFM with a dude who isn't hung, though, as I would get bored. I'd prefer the dude had a sexy ass, because I like to see a dude's ass when he's drilling pussy. The sexier the male ass, the more stimulating.
But in the end, it's mainly about dick size for me, with dude. I've had this fetish all of my life.
Would I interact with the dude sexually? Probably little contact. I might slap his ass when's drillin' pussy (if he's comfortable/on joking terms, etc). That would be a big turn-on, or grip his balls and laugh when he's inside her tight pussy. But that's it. I am not into sucking each other's dicks, ass sex (nor with women), etc.
^That's why I'm 20% gay, and not scared to admit it. If there is no woman with me, my 20% goes in hiding.
The woman must have big titties! I don't like shaven pussy, either.