Have you looked in the Dell MIBs for PowerEdge? You can download those off the server Drivers & Downloads page under Systems Management. I think I have seen some non-server MIBs in there.
Hi Pete, for some reason the MIB doesn't yet show on the Dell support website. I think it's in a queue for uploading. Until then you can use the one in the attachment of the previous post which is the latest and valid MIB.