yes, there is a mini cage in the high limit area. in fact, sometimes around 3-4am they close the main cage on the main casino floor and only the mini cage is open.
in all the times Ive been to Rincon, I think I was in the diamond lounge only once. I usually arrive at Rincon about 11pm and leave around 5-AM.
And to be honest, I rarely have gone into the diamond lounge at Caesars because they cut back on the hours, and I now bring a netbook to use and no longer have to use their computers to check my email (or the business center). Another reason I don't go into the DL at Caesars is that their food offering is weak. when it first opened it was good, but like everything else in Vegas in the last couple of years, things have been scaled back.
in fact, the 7 stars check in area used to have a room with a buffet, bar, sofas, TV but about a year and a half ago that area was turned into offices.