Yup, watch the stipulations. They enforce the PFD rule b/c they fall under Utah state law on the matter somehow, so they it's really a state law the BLM guys are stuck with. Don't assume that they won't read the label. They don't always, but they do often.
Inside scoop on alterations: No stiching allowed; gluing a patch on is ok b/c you don't break through the fabric. I was present when Alvin (the head ranger) said this to a group of trainee ramp volunteers.
As for the rescue PFDs that aren't USCG certified, that rule sucks, but the BLM guys are not unaware of the switcheroo people try. Just remember that it's about a $200 fine and you could get blacklisted in the permit program. The guys at the ramp are just doing their job; if you are later caught wearing a non-approved PFD, you made the right choice for safety and they will know that. Be penitent, have a good attitude and you're likely to get a word or letter of reprimand at worst. Lobby the Utah state gov't if you hate the rule.
Also, to the best of my knowledge the guy who died at Skull in 2001 was not wearing a water skiing vest but USCG-certified vest. He died b/c he was entangled in a rope. The raft went downstream, he went into the Room and was held just under the surface by the current. His family later unsuccessfully lobbied the state for a rule requiring all PFDs to be sold with a knife.