Correct, same chassis used by many vendors, quantum overland, dell, ibm etc. same physical controller but a checksum to prevent others firmware from going on.
I don't know about the chassis, but I do know that library drives that Overland sells aren't locked - they use generic IBM firmware. This is actually a minor PITA for me because I got a NIB Overland LTO6 library drive for $795 and put it in my Dell-branded library. I have to wait a little bit after Dell releases new library/drive firmware before the generic IBM drive firmware shows up on the Overland FTP site.
Back to your chassis question - I have no idea if this will work (or cause a problem that isn't easy to correct), but you can find the Dell version of the library controller card all over eBay (part numbers 73Y16, MU355) very inexpensively (the first 5 listings were under $20 each). When you change that card in a Dell library, the front panel asks you if you want to use the settings from the library or the settings from the new controller card. This might let you change the brand of your library from HP to Dell. That doesn't help with the drive(s), though.
A while ago there was a blowout on IBM-refurbed Dell TL4000 chassis only (1 power supply, no drives, but with magazines and rack rails) for $275. I got 3 of 'em and they all appeared brand new. Every once in a while something low-priced comes along -
this [real link, all others are auto-inserted advertising] is a Dell TL4000 w/ dual power and 2 LTO3 SAS drives for $375 OBO w/ free shipping.