They have decFatigue variables set to 10, 20, or 30 (for small, normal, and large), and time set to 1, so I assume it's per second recovery. There appears to be no difference between "recovers the Vitality" and "increases the Vitality recovery speed). All the ones in category A actually have decFatigue set to 30.
I'm not sure how much fatigue one vitality orb is, but we could possibly test it using meso generating familiars (small and normal amounts using 50 fatigue, and large amounts using 100 fatigue with interval set to 600000, so it might take a while).
Also, I just went into the Empress lobby, after a rather lengthy round of bossing prior, leaving my wolf with like a third vitality left, and my wolf's vitality orb was full again, so it could be that changing channels will refresh familiar vitality anyway. Worth looking into.
I'm not sure how much fatigue one vitality orb is, but we could possibly test it using meso generating familiars (small and normal amounts using 50 fatigue, and large amounts using 100 fatigue with interval set to 600000, so it might take a while).
Also, I just went into the Empress lobby, after a rather lengthy round of bossing prior, leaving my wolf with like a third vitality left, and my wolf's vitality orb was full again, so it could be that changing channels will refresh familiar vitality anyway. Worth looking into.