According to GW fluff, it's the huge amount of METAL in the armours the thing that interferes with the spellcasting abilities of sorcerers.
Being a BONE helmet, I can't see any reason why it should stop a skink from using it.
AND, as Mithras says, a skink is a priest, not a wizard.
Anyhow, if it is in it's approved weapon/armor list, I for one will say that he can use it without problems.
Best wishes.