Hi I had dark paneling in my kitchen and it wasn't in very good shape, lots of nails holes etc. I didn't want to spend the time and effort of spackling all the holes or filling in the grooves, so I did the following.
First I painted over it with Kilz. I made sure it wasn't an oil based Kilz since I was going to use latex paint. Kilz in an excellent primer (cover coat) to use on dark colors. Then I bought a box of medium texture and stirred it right into the paint, then rolled the paint on the paneling. It came out with a rough texture and covered all the holes. It didn't matter that the grooves weren't filled in cause the whole wall just looks textured. I did this on three of my paneled rooms and they all turned out great. One note of caution, you have to keep stirring the paint to keep the texture from settling. Hope this helps. Good Luck.