Unless otherwise specified (such in the case of Loremasters) each wizard (non-allied) in your army gets to pick one spell from the relevant spell lore (Core Rules, 27.0 and 27.3.4)
I don't get your examples and from their wording I think you might be playing the skill wrong.
Scaly skin subtacts 1 from the damage of each attack, so the number of attacks doesn't really matter only their damage characteristic. In you first example the alpha has an additional attack but each attack is still only 1 damage so scaly skin does not apply.
Soo:
1) If your enemy rolls 11 hits and then 11 wounds, all of which are damage 1, you roll 11 saves and for each fail you suffer 1 wound.
2) If your enemey rolls 11 hits and then 11 wounds, all of which are damage 2, you roll 11 saves and for each fail you suffer 1 wound (scaly skin reduces damage by 1)
3) If your enemey rolls 11 hits and then 11 wounds, all of which are damage 3, you roll 11 saves and for each fail you suffer 2 wounds (scaly skin reduces damage by 1)
and so on...
4) If your enemey rolls 11 hits and then 11 wounds, all of which are damage D3, you roll 11 saves and for each fail your enemy rolls a D3 and you suffer an amount of wounds equal to the result -1 with a minimum of 1 (so 1-2: 1 damage, 3-4: 1 damage, 5-6: 2 damages)
So no, reducing the number of wounds by a third before saves would not be equivalent.
Bottom line: when scaly skin applies, for each successful attack, check the damage characteristic. If it's greater than 1, reduce it by 1. This is the amount of wound you suffer for each failed save.
