From my observation CS is constantly struggling satisfying one of two servers. If HS is being filled, Jail suffers, if Jail is being filled, HS suffers. Its a constant struggle. I'd find away to solve this first. I know CS wanted to start a Fill Server Captain program and I can only advise as one of the TF2 captains, that if that person or group of people start to rally the troops you go and help or respectfully decline as opposed to having to struggle with being told "nooo go to {jail}, leadership will take it away" on global chat where your peers can see this. This starts a favoritism discussion battle over global and It makes it harder to achieve the goal of increasing the rankings and getting the servers filled.
Ideally, If you are filling, you'll get pubs to flock in to the servers in need of filling like HS and you now have Jail to concentrate on and have fun. Looking at GTTracker, it seems HS has mostly Afternoon activity, but not really to the point it fills and dies. I'm guessing people get bored so with that I would motion towards a Rotation Server as flamelauncher11 suggested previously in another thread, HS might be a good server to experiment this on and I truly believe that that server would benefit overall from it, for those that like HS it wouldn't be really gone, you could always mapvote for it.
Last suggestion, Offer incentives for being in the server. and filling it. I remember one of my first times Killroy gave away CS:GO goodies. I think even jail credits were given out at some point.
