Well, you might think they can be used, but this notice on the Selecting a byte order shows that they're not actually so usable:

It is important to note that the Berkeley DB access methods do no data conversion for application specified data. Key/data pairs written on a little-endian format architecture will be returned to the application exactly as they were written when retrieved on a big-endian format architecture.

Thus, if I'm getting it right, you can actually read a BerkeleyDB file from a different platform, but first you'll have to convert both keys and data to native form in order to use them.