Following enchantment seems to work
Fortify Health (Although this enchantment seems to conflict with dark soul perk)
Fortify Stamina
Fortify Magicka (AI might not allow it to be used properly)
Fortify lightarmor (confirmed via getav damageresist, presumably fortify heavy armor will work as well)
Fire/Frost/Shock Resist (confirmed via getav fireresist)
Following enchantment has been confirmed to not work
Fortify onehanded and fortify arhcery. I had a forsworn glove that give 132453% fortify onehanded and fortify archery, and the thrall is only doing 200 to 300 damage
Fortify spell school. It will not reduce the charge cost on staffs and enchanted items
Fortify Health Regeneration (does not work at all, thralls seems to have their health reset every time you move to a new area)
I couldn't test fortify magic resist as I could not find a thrall that would consistently use a shield.
Couple of things I noticed
-Sometimes enchanted effect will not be applied until you have moved to a new area. This means if the thrall put away the shield then put it back on without transitioning, the shield enchantment affect will not be applied.
-The charges on enchanted weapon that the thrall is wearing might reset when you move to new areas, ie, the become fully charged. (needs more testing to confirm this).


). Also I usually don't like starting new characters by grinding trade skills; its hard to keep enthusiasm alive.
The only reason you might NEED a high Alteration skill as a pure mage is to get the last rank in Magic Resistance, anyway... for a Spellsword that likes to get close, Dragonhide can be very nice if you haven't been smithing up your armor, or are going armorless -- an infrequent build, to be sure. It's just so nice to have a good damage resistance when you are fighting up close... much less instant-player-death that way.