The legal acquisition for a suppressor is the same as for a full-auto weapon. $200 tax stamp and the full BATFE routine.
I watched Zak Smith shoot a suppressed .308 on steel at Whittington. Much quieter than without a suppressor. Maybe more like a .22 rimfire from a 10/22.
To a hog at 100 yards, odds are that the sound of the bullet strike would be louder than the muzzle blast. Could be that other hogs wouldn't know the direction from which the shot came, being more focussed on the sound of the bullet strike. Maybe...
You're from BATFE? Come right in! I use all your fine products!