If you want SAG actors your production must be a SAG signatory. I say your production - not your company. Example - you decide to make a short film - that short film must come under a SAG agreement to cover the talent.
Sure, a SAG actor can be naughty and just work for you - it's really his problem not yours - but he faces a host of trouble from SAG.
Actually, my wife is a SAG actress and I use her all the time in my stuff without asking SAG. I figure if I have to check before I film my wife SAG can go piss up a rope. But she could get in trouble, theoretically.