Well, they have a 97% chance of resisting being hypnotized, so the odds are definitely against that working out for anyone.  I've found hypnotizing a great tool for either building up my army or simply deflecting attacks during a battle (AI almost always goes after the defecting unit with a vengeance), but I only go after units with a 30% chance of resisting. 

I have hypnotized pretty much anything

including a group of 3 stalkers . But that's

nothing ; I have also caught Vetrar and

Aegethon. I was testing the game's "honesty"

(some stats displayed are far from being

accurate, such as... accuracy, by far the worst).

But the 97% percentage is true : you do have

 that 3% chance of catching a monster... but

it obviously will take a lot of reloading, which

is not fun at all.

It has probably been pointed elsewhere that some

units are NOT safe to catch, at least for now. Any

Sorcerer King unit (oh... those  awsome Shadow

Commanders... Scouts.. . Warg Riders...) are all

bugged. You take them (after reloading the whole

day) aaand then you find out that as soon as you

reload your game after getting them, they appear

in your army as duplicated and impossible to delete.

And that extra unit won't work in battle, block its

own turn, stop the battle and force you to auto-resolve.

And you can't ever erase it with the "delete" key. You

then have to dump the unit somewhere and never use it

again. Oh and if you have stationed your army including that

unit inside a city.. . You're never getting out !!

However, although all the SK-specific units have

that same bug, as I said Vetrar and  Aegethon don't.

So enjoy !!!!