I recently found this .asi mod around. This file fix the bugs about hairs,beards and others alpha textures. Working for peds and objects. I tested it and all my models are fixed now.
You just need Cleo library to get this .asi file working. I have Cleo 4 here so i didn't test it on Cleo 3 but it should work just fine.
Extract it on your main directory, delete your SA.exe and use the compact one. Otherwise, your game will crash!!!
Silent Patch LINK
San Andreas Compact exe
I did not make this mod! I'm only sharing it since it's annoying have alpha bugs in game.