There's nothing to stop them offering a seg account to professionals, but it isn't normal practice. Margins in professional business are generally much slimmer, so mean (especially in thsi environment) that they don't want to have to borrow money to post your margin. Keeping funds non-seg means that they can pass your funds through to meet your margin requirements. Asking for professional rates and private client protection is likely to be seen as having your cake and eating it.