Hostages are specifically disallowed for bank robberies because of several different reasons.
1) People volunteer to be hostage or have their friend be hostage then split money later (clearly fail)
2) With the hostage, the situation almost never ends, it gets dragged out to where it is inevitable for the bank robber to collect the cash, and even if they die afterward, no biggie, they don't lose the money.
3) Hostages tend to take the guns of fallen robbers (if a gun fight breaks out), which even now with having it limited to one gun, it would not stop this behavior.
4) It has a tendency to cause more troubles for everyone involved, since hostages move all around and don't act as if they should be afraid for their life (like a real hostage would be) so they get in the way.
etc. So hostages are not a good thing as far as I am concerned, yes it would help you earn the money, but it's never supposed to have been easy to rob the bank as it is quick large amounts of money that you can earn from doing it.
Anyways, if there were 10 police and 4 SWAT, it is possible to win with 7 of you, but also, if police are in those numbers, it's probably not a smart idea to rob the bank in the first place obviously. Which is why being able to see how many police, SWAT, etc jobs are taken, was removed, as to enhance your ability to assess what your chance you may have, instead of just checking a value in which you would be unable in real life to know as this is serious RP.