It would be redundant for cased greaves. If you're doing the floating / schynbald greaves, I'd suggest trimming off the front of the legs and putting laces there. You can tighten the mail legs that way, and the greaves will cover the laces without the extra weight of the mail on the front of the legs. For cased greaves, chop the mail legs at slightly below the top of the greaves.
Sabatons are almost completely dependent on the footwear that they go over. So if they're built for those shoes, no problem. If they're built for modern shoes with wide soles, they won't work as well ... they'll still "work" in that they can go over top of it, but they'll be floppy, shift around, and probably won't be comfortable either.