Profile edit userid

[Grouper]

I am wanting to create a script that will run on a hidden (hidden to user, but not admin) field when an admin updates a users profile. What variable would I use to get the profile users id instead of the admin's id that is editing the profile?

$vbulletin->userinfo['userid'] is for the user that is doing the editing right?

EDIT: Also should I use the profile_updateprofile hook or the userdata_postsave hook? Again only admins will be able to edit this custom profile field.

I have a similar script that processes this field on registration. This field can be edited only on the registration page by the user. I don't want the scripts to overlap and run over each other.