I've dove both Vortex and Morrison. Vortex will check for your cert. card for sure. Can someone fax you a copy or fax a copy to the dive shop there? They might take that. I don't think they checked at Morrison. I liked the dive at Morrison better. But if the river is up, you can forget good viz...it will be lame. I don't care for Vortex that much. As it is said, "The best springs in life are free." For what it costs to dive Vortex, I'd rather be diving off a boat in Panama City in the cold, choppy gulf at this time of year. Either way, I hope your dive goes well.
As far as that warning sign goes, I saw no snakes or alligators there in October, which was the last time I dove Morrison. Got into some hellacious fire ants, though, when I took my booties off. That's another story for another day! Even if there were slitheries and gators in there, I would have still dove. That day had some
fan-smacking-tastic viz, probably the best for freshwater diving I've done.