A disk dump device can only contain a single dump at a time.
Tape devices can contain multiple dumps.
LOAD DATABASE WITH HEADERONLY would probably be the first thing to try to get information about what is in the file. (see Commands Reference Guide:load database) It won't give you anything for a dump device created using the dump database to "compress::<filename>" method though.
I'm not sure what it would give you if run on an incremental dump file.
-bret