Jorge Ortiz started a project called Linter a couple of months ago, running as a Scala compiler plugin. It doesn't do much yet, but it catches a few common mistakes. (The type mismatch checking rules for == and contains have equivalents in FindBugs, if I recall correctly.)
http://github.com/jorgeortiz85/linterI'm impressed by how short the code to handle those few cases is. (It almost makes writing a compiler plugin look easy!)
Unfortunately, since he announced it a couple of months ago, nothing has been committed on his branch.
HTH,
Michael