I've seen some adapters like pictured above where the SATA connectors are -not- aligned properly for a hot-swap backplane. I ended up purchasing a six drive (2.5") dock and installed it in a free 5.25" bay after trying two 2.5"-to-3.5" brackets that didn't align things properly. Easiest thing would be to see if your manufacturer has a 2.5" tray for your particular hot-swap unit. Sometimes the trays and the connectors on the backplane place the drive connectors offset so something like above wouldn't work.
