if the original question is whether a journeyman professional golfer (as opposed to golf professional) has some advantage to handling the pressure, i think no. I REALLY think the golf pro has no advantage.
i think its unlikely that, coming down the stretch, a guy who played some mini tours but never made the show is saying something like "this pressure here in the US mid-am is nothing like what i faced during my pro days", nor is he saying "boy, i won the Hooters greater white plains open, so winning the mid-am and going to the masters is no big deal".
being an am might be less pressure than being a journeyman pro and eating hot dogs out of the back of an RV, but thats really a matter of the quality/stability of one's day job. I know i'd be saying that playing the mid-am beats working at my job any day.
only guy that might, in my view, have an advantage, in my view, is a guy who has won on a major Tour. Dillard Pruitt, for example. Even in a case like this though, i think playing for a national championship is a little different.
i think the reinstated am phenomenon is really a reflection of the fact that, since at least the late '70s, the pro tour has offered a good living and anybody who had a fighting chance to make it tried to do so. i dont think there are too many guys who passed on the tour are wonering what might have been (WISHING maybe, but not wondering)
the reinstated ams are just better players., and i 'd gues they were better players before turing pro too