I wouldn't Wavedash in slow motion, the ONLY reason you would want to do that is see how it looks when you execute it. It would just be better to start quickly, I can actually do WD in normal time but not in slow motion. It'll just screw with your timing.
I can see where you're coming from, but it won't screw up your timing unless you exclusively practice in slo-mo (which would be silly). wavedashing is a rhythm, and once you obtain that rhythm you can execute it at whatever speed you want. I am tempted to suggest that you would be even better at wavedashing in real time after mastering it in slo-mo, but I have a bias as it's really been working for me lately
now, you also mentioned seeing how it looks in slo-mo... I believe this is an important element of a properly executed wavedash; it gives you a fuller understanding of how your character moves during a wavedash, and what a properly executed wavedash looks and feels like. it helps your brain wrap itself around the concept even more; the more angles you have on it, the better you understand, the more mastery you have over it.
also, because you're going so slow, it gives your muscles the opportunity to relax while executing wavedashes. when you go back to real time, your muscles remember this too. even if it doesn't help with your timing per se, it's just good ergonomics. for instance: before I started training in slo-mo, I tended to hit jump and then fully depress the shoulder button at the moment I wanted to air dodge. it often led to flailing fingers, muscle strain, and missed techs. now, even though there are only a few frames between hitting the jump button and going airborne (ie, given the opportunity to air dodge), I can use those frames to depress the shoulder button and THEN click it in when I'm able to execute the dodge. smoother wavedashing, less muscle strain, bigger balls.
tl;dr everyone learns differently, but there are definitely benefits and I don't think anyone should be worried that slo-mo will screw up their tech skill. it is simply another tool in yer box to help you pwn nubs.