From my testiing, if your spirit mend is on CD when you pop stampede, the spirit mend heals don't work. That's in spite of the fact that, if you summons a new spirit beast while spirit mend is on cd, it does work.

Anyone able to confirm or refute this?

If it's accurate, you obviously need to be careful only to pop stampede when spirit mend is off cd.
Edited by Arrowset on 10/6/2012 10:57 PM PDT