IIRC, Spirits of Moment are bound to a specific skill. You can use it on all units having the same skill to level it up. That means, if I'm not wrong, that you can use spirits bought on Rowanna's revival on others units than Rowanna if they share the same skill.
And I might be wrong, but I remember reading that the skill up has 100% chances of happening. Take this with a grain of salt without another confirmation though.