The only reason a prop firm would require a 7 is for RISK CONTROL.
When I traded with Schonfeld Securities, 99-2004 the just started to require a 7 for all new traders. They were fined for a minor fraction before that. Hence, having all prop traders with the 7, the buck stops with that trader if they do any 'Rules" breaking. The firm is off the hook, so to speak for the most part.
I raise millions of dollars a month for venture projects, I was required to have the series 22 while at a Firm with a brokage end of things. However, now that I am an officer of the Capital Raising team (My own LLC and a Partnership with another Rain Maker), no lisc. is needed. We do not deal with any "Securities" as defined by Rule 144 Reg A for the most part and still only deal with sophisticated investors defined by Private Placement rules, to play it safe anyway.