I have to say I like porn, but anyway wouldn't mix it with swinging, at least not right in THAT moment nor right before that.
Unless being a product well devised for this sort of scenarios (which could exist but I didn't saw anything like this, except perhaps with true amateur home made movies, and perhaps European movies made in the 70's that are pretty much amateur like), today porn is grounded on models, both for the physical aspect the actors/actresses have, and for the activities they engage into, at last, they follow the lead of what society (most males) likes to watch and avoid what they dislike to watch (e.g. wearing condoms) and end up imposing a view of the sexuality that doesn't have to do with the real sexuality. This may trigger anxiety on the attendants to the meeting, beyond the proposed turn on: from competitive feelings to a reminder of insecurities (for example, about your body, not being the TV model, performance issues, and so). Even when not enough to ruin the night, this anxiety may make the experience less enjoyable to someone, and precisely because of the fear to admit insecurities (moreover if they doesn't know the other people involved), they may prefer not to tell and let the movie roll.
So, unless all the attendant knows well enough each other as to ensure they can deal with this eventual issues, I believe it's a bad idea. Or at least, something to think about when choosing to watch porn.