I had the semen and tried a number of times with no success, despite having a mare that was good with frozen semen and a great repro vet. I sold the last of it and the buyer's mare is pregnant with it. I know of quite a few pregnancies, despite my own bad luck. I guess it depends on karma (just kidding).
I tried it twice and did flush one embryo on the first try. The embryo didn't stick in the recp mare and we got no embryos from the second flush. Since the semen looked good both times and it did work once, I have to say the semen does work.
Mobility isn't the entire equation to "good semen" but at least you can tell it gets around quite well and there arent many dead ones.