If it is orginal, it is most likely teak. Teak wood is used widely because it contains alot of oil. Personally I find teak oil the best to make it look good a perserve it. I think that being oily, varnish doesn't stick well and when it starts comming off, it's a pain to restore. With the oil, all you need to do once a year is clean it with a teak cleaner and re-oil it. The holes are cosmetic, but if you want to plug them, it's probably best to use a wood plug. You can get teak and mahogany plugs from West Marine - Make Boating Better with New Boating Gear from West Marine
Old weathered teak is gray in color. It will have grainy grooves where the softer wood has oxidized. It dries up, but I don'y think it ever rots. When you sand it, it will form a dark red/brownish dust. The West Marine site will have lots of pics of teak. Make sure your teak is good and dry before you oil it.