Distributing the dbpro dlls outside a dbpro exe will be copyright infringement.
You don't have to be too inventive to get around that though. You could distribute a dbpro exe that does nothing and source the dlls from there.
Or use the method used by IanM's no longer available interface libary. Have a dbpro exe that just calls a tpc dll. The dbpro exe then gets everything running before calling your dll. You can call all the dbpro functions from your dll.
I wrote a clunky program that used the second approach so you could use dbpro functions in .net dlls.
http://winch.pinkbile.com/net_int.php
Basically a poor imitiation of IanM's interface libary but allowing you to write in c# or vb.net instead of c/c++.
There is also some intreasting info on this site.
http://dbp-unchained.tk/
By way of demonstration, he emitted a batlike squeak that was indeed bothersome.