Dame!
This is one of the articles I read that had me start this discussion.
http://www.otocinclus.com/articles/snails.html
"Snails mainly eat detritus (fish wastes), dying vegetation, and algae."
I don't think they will do much on the sawdust. Even if they do, you'll probably need to cover the substrate with snails for them to be able to keep up with the waste produced by most plecos. Mechanical filtration is still pretty much the only way to attack sawdust poo.
is it ok to leave the sawdust in there for periods of time? i have my tank barebottom but the sawdust still piles up quicker than i can take it out without daily water changes.