No they can't. I think they have order of magnitude of 10bn of their own money in their good strategies (Medallion et al), and another 10bn-ish of external money in their bad/stale strategies (which are still among the better hedge funds and can charge 1%+10).

But reputedly they neither allow external money into Medallion nor do they let employees compound their existing stake in the fund but pay out ginormous 20%-40% annual dividends exactly because the strategy is not scalable.