I don't think Explosiive Arrows' damage is boosted by ANYTHING besides the skill level, not even Destruction or Way of the Ranger.
But I just tested it in game so...
And no, they weren't critical hits. Destruction DOES boost Explosive Arrow damage, nothing else does. If you want to see it for yourself, it takes like 5 mins to start a new FoV game, buy a bow, find an enemy.
Anyway, I'm pretty setup on a mage/ranger hybrid
Max Fireball
Max Firewall (FoV)
Max Battle Mage
Max Destruction
Max Explosive
+ assorted skills
~max vit & dex.
The great thing about it, is that I can swap between regular ranger (EA, SPLIT, WotR) and the mage hybrid at any time.
Mage pet
Stick bow full of crit ench
Armor with mana
Jewels with life regeneration
Charms to max with vit & dex, rest spirit
Good to go!
I think the best mage spell combination would be Magic Missile + Fireball, but I'm going all fire for style reasons, plus magic missile tends to eat mana rather efficiently.