Nok Air does similar deals, flying DMK-CJM (Chumphon) or URT (Surat Thani). I've taken Nok Air out of Ko Samui (right around New Years, so USM flights were stupidly expensive). It's fine, though it blew most of a day in traveling (8 am ferry, didn't get to Don Mueang until 4 pm or so).
One thing to note is that your wedding party would be doing a cross-city transit in Bangkok from BKK to DMK, on what would likely be separate tickets (so missing the flight probably means a new ticket, or possibly an overnight stay to catch their breath, since they'll have been flying for a good long while). How comfortable are you or they with that?