For the most part no. If they are traveling for leisure or commuting, they are NRSA's (non revenue, space available). This means that they only get a seat after everyone who wanted to standby has gotten on, and all upgrades have cleared. In other words, if the plane would go out with empty seats, they would get them. The exception is when they are transferring to a different station for work. For example, if a pilot is based in ORD, and has his first flight out of DFW, he would be confirmed on this flight, I believe in F, as the union contract specifies. Never would a leisure traveling employee get priority over a paying passenger.

Of course, there is a very, very small chance that all of those FA's were travling to the US for their next flight, since for some reason they were not needed for the return. In this case, they would have to be confirmed onto the flight, and it is quite possible that the union contract stipulates that it is in a premium cabin.