Vanitygen isn't a bruteforce tool, it can't search full addresses, it's only for generating "vanity" addresses.
Basically it is a bruteforce tool that could potentially bruteforce whole adresses.
When in doubt, check
Wikipedia's definition:
In cryptography, a brute-force attack consists of an attacker submitting many passwords or passphrases with the hope of eventually guessing correctly. The attacker systematically checks all possible passwords and passphrases until the correct one is found.
I'd say you can never have any hope of guessing the complete private key for a certain address correctly, so by this definition brute-forcing isn't possible.