[Diablo 3 Guide]This test was done in reaper of souls beta with partner. The equipment is as the picture shows. The chest item is Immortal King's Eternal Reign.  

Test one: Is Iron Maiden & thorn damage efficient to life on hit effect?

Iron Maiden: Get 6102 thorns
Regenerate life per sec: 0
Health: 137036
Life on hit: 810
Result: Iron Maiden thorn damage can not trigger life on hit effect

Test two: Passive skill Holy Cause. Will weapon with holy damage influence life on hit?

Holy Cause: Your weapon holy damage increase by 30%. Each time you cause holy damage to enemies, you'll get 1% maximum life recover.
Main skill: Shield Bash, the fifth rune
Regenerate life per sec: 0
Health: 137036
Life on hit: 0

Use three weapon to test: flail with holy damage, sword with holy damage and normal axe

See the test data from the table below:

(The negative number -255 in the table: blocked by enemies and be hurt)

Result: Every weapon can get life on hit no matter with or without holy damage

Because the selected main skill Shield Bash has holy damage, we changed it to Slash and tested again.
Slash: Ignite the air in front of you and cause 190% fire weapon damage
Result: Every weapon cannot get life on hit no matter with or without holy damage

Now it seems that life on hit effect is not related to weapon but to skill holy damage. To proved that, we conducted another two skill tests.

Fist of the Heavens
Summon a lightning pillar to explode, deal 440% lightning weapon damage to all enemies in 8 yards. The explode makes 6 charged arrow shoot out and deal 320% weapon damage when through enemies.
The 2nd rune Heavens Tempest: Summon lightning storm cover the area in 8 yards for 3sec, deal 25% weapon damage to enemies through the area each second. 

Result: Sustained damage to target and life on hit continuously.

Heaven's Fury
Summon fury ray with holy power, deal 1260% holy weapon damage to enemies be hit in 6sec.
The 1st rune Blessed Ground: The ground irradiated by the beam become holy land and deal 975% weapon damage to enemies walk through in 5sec.

Result: Sustained damage to target and life on hit continuously.

Conclusion: 1) Iron Maiden thorn damage cannot trigger life on hit effect
                   2) Holy Cause life on hit effect is related to skills with holy damage, not weapon