Parallel pg_dump on a single database

Is it possible (or smart!) to run multiple pg_dumps simulataneously on a single database, dumping different parts of the database to different files by using table and schema exclusion?  I'm attempting this and sometimes it works and sometimes when I check the dump files with 

  pg_restore -Fc <dumpfile> > /dev/null

I get 

  pg_restore: [custom archiver] found unexpected block ID (4) when reading data -- expected 4238

I suspect that locks are colliding sometimes and not others, but I'm not sure.  Little help?  

Thanks in advance,

Bob Lunney