It is said that no non-creative card is 100% Soundblaster Pro compatible (while many cards claim to be), but if this is true, I'm not sure what those incompatibilities consist in.
Nope, this is a mix-up. It is said that no non-creative card is
SB16 compatible...

There are dozens of working SB Pro clones available, because Creative licensed the design to other board manufacturers. Many of these sound better than the original SB Pro (less noise), and often come with a real OPL3 plus wavetable header.
Non-Creative cards compatible with SB16 are very rare, but they do exist. Check out
this excellent thread on the VOGONS forums for more information.