I have been trying to find a product that will prevent my OWB revolver holsters from absorbing rain water when I'm outdoors for a few days in the rain.

I have been reading that SNO SEAL will do the trick but I'm wondering what the negative side effects might be.

I would be applying this to holsters which have already been cleaned using saddle soap.

What other products might work better?

Personally, I use Obenauf's Heavy Duty LP and Obenauf's Leather Oil on everything leather.  This includes Crossbreed IWB holsters, belts, boots and everything else.  It seems to leave a nicer to the touch surface on the leather than Sno Seal and does not get on my clothing or hands after it has been put on and absorbed.

SNO SEAL is awesome on boots, never put it on anything else.

I have a jar of it I use on my boots, interesting thought to use on holsters. Interesting in hearing whether it works as well on them.

Edit: the only thing I can think of off the top of my head that might bother some is it makes my boots alot darker.

Obenauf's, Pecard's, and Sno Seal all work very well at protecting leather. Pick one and be happy. I prefer Pecard's.

I've used Sno Seal on boots and homemade knife sheaths that don't have have detailed molding.  I'd be reluctant to use it on boned leather in the same manner.  To really get the most out of Sno Seal, you need to heat up the leather and let it absorb the Sno Seal.  The process may change the characteristics of the leather enough to affect any detailed boning/molding as it soaks up the Sno Seal.  If it's only lightly molded (such as those offered by Simply Rugged and El Paso Saddlery, for example), it would probably be okay.  Sno Seal is basically bee's wax which has been used for waterproofing leather for a long time.

Agreed ^
I'll add that if your just looking for water "repellent" it will probably well since u have it on hand already.
  If u happen to have a spray gun you could purchase products that are designed for this purpose. Work best if they are sprayed on. Some guys dilute them and dip the entire holster or sheath too.  As long as you don't mess with it until fully dried it will be fine.
   I even had an old timer tell me once that he uses a 50/50 mix of water and Mop n glo! Either sprayed on with a paint gun or dipped or even sprayed on carefully with the spray bottle it comes in but that will probably leave spots.
   I didn't believe him so I tried it on some scrap once. It actually worked "ok" not the best obviously but water did bead up on the leather after and didn't soak in right away.

  Anyway after I finish a sheath or holster I like to use a very thin coating of kiwi neutral shoe polish. Any make will probably work. Just adds to the finish a little bit and makes it a little more water repellent.

Orherwise give a call to Springfield leather company. Super nice people. Tell them what u want to do and they'll hook you up!