I would warrant that ALL the MIDI devices are functional.. but...
Based on what I've read here, and my own experience over the years with MIDI interfaces on computers, some flat out don't work with the Axe. It may be due to all the sysex data being passed back and forth or that today's OS'es are W-A-Y faster than when the MIDI spec was written. REDUCING the MIDI Buffer size and INCREASING the delay time can make many of them work, but not all.
IMHO - I believe it boils down to how much [sysex] MIDI data the Axe can process without choking. I say that 'cus I've not ever had these kinds of issues with other MIDI devices, even when hooking multiple different vendors in-line using MIDI THRU. I've tied Roland, Korg and Yammy together before.. Mapping was a b*tch, but it worked. Most - if not all- of that MIDI data was PC/CC driven, not sysex.
Again, it may simply be due to the huge volumes of Sysex data the Axe uses.
I currently have TWO Midisports... UNO and Anniv 2x2. Despite all the problem written about the UNO on this forum, I have not had issues with it. On the flip side, most of the feedback on the 2x2 is positive on this forum, and I'm experiencing issues with it.