yes you can.....
step 1 - learn to make a DLL
sounds simple, and really it is.
BUT:
You'll need to research a bit on there site to properly configure the compiler to make DLLs. Thats the hard part (assuming you know C++ code)
step 2 - code a DLL for DBE or DBPro
its like any DLL except DB used CDEC instead of STND Call.
Check on C++ namemangling for how your function will be called.
There is a compiler option to dissable name mangling, but you'll have fun trying to find it.
step 3 - Make DLL a plugin
This just means making a string table for your exported functions.
See DBPro docs on parameter listings and verify C++ name manglings.
example source available here:
http://darkbasic.thegamecreators.com/?m=forum_view&t=26215&b=6