Nerites will eat algae on glass but probably not all of it; sometimes you can see little squiggly lines where they've eaten some algae just in a little trail. Any living creature will add to the bioload. I like snails, but it's probably easier and more reliable to just use a scrubber to get the algae off. I saw in another post of yours that you are thinking of adding more otos; these will also add to the bioload and moreover are usually all wild-caught and are known to be difficult to transfer to aquariums without losing a few, so that's something else to think about. If that algae on the glass is hard then otos will not eat it but nerites will, but like I said not necessarily all of it. Again, any creature you add to the tank will add to the bioload.
