It shoould fire for the secondary usergroup, but you have to keep this in mind:
only one event per action and currency will be applied, and the "best" (most positive) one is the one that gets chosen if multiple events are legal for that user.
Basically, if you have additional events for the same event/currency and the only difference is the usergroup, then the one that qualifies for the primary usergroup beats the one for the secondary usergroup if the primary one was worth more.
does that sound like the case?