not original battery- can I still get core refund?

The only part of the core that they want back is the stack of modules with plastic end caps and four metal bars to hold it together... People who rebuild packs will sometimes modify the cover of the pack with paint and their own logo, but that's not what you'll be returning. There's almost zero difference in that actual core you're returning versus an original OEM pack unless your core is a newpriusbattery.com pack, which haven't been around long enough to go bad yet. In pic below, the big block of modules on the left is what they want back. Everything else you keep.

 

PS: buying new bus bars and nuts is wise. Also if corrosion is really bad replacing voltage sensing wiring harness is wise to do while you're in there... You can get good brand new harnesses on Ebay for less than $100... Best quality and price on bus bars comes from these folks: New CNC Machined Hybrid Battery Bus Bars - Reflex Concepts LLC and best quality and price on nuts I've found is from these folks: NSPIN5X12YLW - Spin Nut Yellow Zinc [NSPIN5X12YLW] - $0.35 : Bel-Metric, Metric Hardware, Metric Fasteners, Metric Bolts, Metric Nuts & Time-Sert Thread Repair

To prevent corrosion in the future you can use di-electric grease but the stuff is a mess to work with and needs to be used as sparingly as possible. It's not fun to work on greased up packs, but if you're going with brand new odds of working on it sooner that corrosion grows are unlikely.

 

toyota dealers will not take back anything but an oem battery with all the oem parts, including case.
if it looks oem, and everything there, they're not bright enough to know better.