I think I played against you today with my melee ranger Zenyana. You run this build with fern wolf right? Seems like a solid bunker style build to me and like you pointed out I think the one real weakness to this build are condition builds that are based on poison "condition thieves, necros, etc." Killing your heals is the name of the game but most people won't expect that kind of healing or resilience from a ranger anyway so you're pretty safe in that regard.
Did some testing and unfortunately the healing power does not help the well siphon life rate. However it does work on a number of other abilities.
Healing power works on:
Dagger - Life Siphon
Focus - Reapers Touch
Well of Blood
Staff - Mark of Blood
Dodge - Mark of Blood (Mark of Evasion)
Does not work on:
Vampiric Rituals Trait
As far as what I got, my regen averaged at 304 per tick with the cleric amulet, 214 without it.
Dagger - Siphon life averaged about (258 x 9) so about 2322 healing on a 12 second cooldown which isn't too bad.
Regarding the traits, the vampiric trait hit for about 25 health each and the Vampiric Rituals trait only hit for about 42 each. Considering that each well only ticks for 5 seconds, thats only [(25+42) x 5] = 332 health you're getting every time you use a well...