I would certainly try to use it. Sand blast or bead blast the inside, then true it up in a lathe. I have personally gotten by with worse looking drums, just needs some time put into it. As far as the seal goes, if it's cleaned up, it will seal, just don't spare on the grease during re-assembly. Brake dust is nothing compared to sand or mud on your bearings. Your seals should protect from any crud getting into your bearings.
RIP - Yamahondaman!! You will never be forgotten!
RIP - Sam Brehm!! Gone but NEVER forgotten!
RIP - Sandpuppi101 - You will live on in my mind - I miss you friend!