Hedge Fund Haircut

Just curious on haircut for hedge funds. As a market maker in options, firms are required to post margin to roughly cover moves in your portfolio >< 15% in the market and also $25 per contract. This is for a medium sized firm making markets under a large BD platform. What are the costs for a large scale, multi $B hedge fund and can they use assets invested elsewhere such as long equity positions, other derivatives and fixed income holdings as collateral? thx

Ouch, no takers. How about this one. When shorting a stock, what is the typical rebate to a fund for the short exposure in a hard to borrow issue same question for a normal borrow stock (so is it negative rebate for hard and positive rebate for reg, or is there no rebate for reg?). Also, same question for options and the premiums given and received for long and short positions (obviously not an issue with underlying borrow concerns). Thanks