The http://www.winehq.com/News/status.html states that the implementation of the serial/parallel port is 90% complete but that DDE is still being implemented by Eric Pouech and not functional.
the status page is now a bit outdated DDE (and DDEML) now kinda work however, some 16 bit support is still missing in DDE (and DDEML), hence your problems as the trace shows as of today : - two 32 bit apps should be able to communicate through DDE - two 16 bit apps should be able to communicate through DDE - however, a 16 bit and a 32 bit app will not be able to communicate
I have a yet unfinished patch here that should (partly) take care of that if you have the wine source and are ready to do some testing, I can provide you the patch to see if it helps in your situation
as DDEML is a pure 16 bit DLL (the 32 bit DDEML implementation is part of USER32), it's very unlikely that native DDEML will work in wine so, sticking to builtin USER/USER32/DDEML is the only viable solution (even if it's not completly done yet)
A+