Yes, that is true generally.  No arrests while Congress is in session.  HOWEVER, IF the Member is being arrested for TREASON or FRAUD.....they can be arrested on the floor while they are voting!  No special treatment for Treason or Fraud charges, which is what we are dealing with here.  Let the round ups begin!  (Actually I think it would cost the tax payers less money, if they are rounded up on the last day Congress is in session, cuz they are all in one place.  Ah, wishful thinking.)