I usually use just one hook. I haven't noticed any problems with the frame. In the rear I've always used the trailer hitch receiver, again, no problems.
If you was to use a sling to 2 hooks it's OK, but make sure you look at and understand table 3 on page 33 of the vehicle recovery manual posted.
And I agree that chains have a place in vehicle recovery, but please make sure you know how to use them before doing so.