We have a B-25 here in town, and I have sailed against a Santana (but I don't know if it is a 23D) for years.
Honestly in all of the boats in this size I find people are much more likely to sit on the side of the cockpit not in it. The heel of the boat just makes the cockpit uncomfortable so people wind up on the coming anyway.
Frankly if you are looking at the Viper, I would also seriously be looking at the VX. It was also designed by Brian Bennet, but is a 15 year newer design, so a lot of the issues that have caused problems on the Viper were resolved on the VX. it is also significantly lighter, a few feet shorter, and the spinnaker launch system... Is about the easiest launch system I have ever used.
The answer for the slippery side decks of the viper is about $10 in non-skid tape. This is a pretty common 'modification' to the viper.