It's a dirty, underhanded way of recruiting and you will just end up with a terribly disorganized guild with all kinds of people you might not want in it.
I got really really angry with random whispers and guild invites being thrown in my face several times a day that I had to block guild invites.
From what I know of this is against the Terms of Service.
I remember reading something about addon scripts or addon exceptions. I don't remember fully but it could also have been a blue post on the official World of Warcraft forums. :s
I remember reading about it because I always got random invites on the Public Test Realm all the time so I decided to see if there was a rule against it.
yea i just love creating a new level 1 character that no one even knows about (completely intended because sometimes i want to play in peace), then boom i get spammed with guild invites when i'm in the middle of nowhere. lovely addon. /sarcasm.