The RS2WC080 supports staggered spin-up. See the features list on page 2 of the Technical Product Specification. You might be able to find other information you're looking for in that document too.
For HDD compatibility, see the Tested Hardware & Operating Systems List for the RS2WC080.
I'm well aware that staggered startup is claimed. That's why I bought the controller.
"power up in standby" is a rare feature on sata drives (even green ones).
I suspect it has not been properly tested on consumer drives, or tested on drives in JBOD mode.