Aladdin dodged the guards attacks but pretty much got fucked by Jafar when he started using magic on him. Clearly this shows thfs avoidance doesn't stretch to magic.
On a more serious note it really doesn't make much sense for thf to get magic evasion if you think about it. Although it'd be handy it just doesn't fit in with our job description or as far as i'm aware the job description of thfs throughout ff games.
If your determined then get a MDT- set to further fill up your bagspace and swap in for nasty -Ga's but out from that just bring a whm and suck it up. :s