As you mentioned, currently the WVD Spectrogram.vi doesn't support complex math. But the good news is that the vi is open source so you can edit it as you see fit. I think this is probably a great product suggestion and encourage you to visit the Product Suggestion Center. Thanks for your feedback!
Thanks for replying to my message. It turns out that for my application a Wigner distribution representation (not quite WVD) is more useful. I needed to write this function from scratch, so while I was at it, I made it support complex math. Now all I need is to get the units to work out - I've noticed that the FFT and IFFT I have to use for these waveforms don't keep track of units at all. I think I will suggest this along with the complex math support for the WVD Spectrogram.