I would make a "combine" validator that combines 2 checks:
-check unit type of caster
-check unit type of target
If they match, it would apply the effects. I haven't done much with the validators yet but I'm pretty sure it's a start. Maybe it will need a "condition" validator in the process as well, to check that the caster and target actually match.
It is doable. Validator "unit type" has field called "other unit". Just select Other Unit - Value as Caster (Unit - Value being target), and validator will compare those instead of Validator - Value (you can leave that one empty then).