Just got off the phone with HP support.
Unless the drive is listed on the QuickSpec they have no clue and won't comment.
The closest drive on the QuickSpec is the 691864-B21, a 200 GB SSD that retails for over $1399.
Interestingly, HP sells the 240GB version of my 200GB drive (the 200GB is overprovisioned for drive life), part # EQ51AA for $700. Market price for the Seagate 240GB is about $316.
But they say that this drive is fine on the hp z620 family of workstations. Here's rhetorical question for the public: If HP advertises both the z620 series and the DL320e series as having a SATA 3, AHCI compatible disk controller and one of them does not work with a SATA 3 drive, doesn't that mean that one of them is NOT really compatible.
For the $1399 HP wants for their rebranded (but unknown OEM) SSD, I can buy an LSI 9207 SAS/SATA controller (about $250) and TWO of Seagate's 480GB Enterprise SSD's. Or I could buy a real hardware RAID controller (LSI 9271-4i) with a BBU and two 240GB class Enterprise SSD's. The only downside is that I don't get the blinkenlights on the front of the drives.
The LSI controller then actually works with SAS drives (hp wants another $100 to enable SAS mode on the b120i), and it gives a full 6 Gbps on all 4 ports instead of 6 Gbps on the first two and 3 Gbps on the second two (again limited on the b120i controller). In benchmarking the LSI controller is 5-10% faster on reads/writes than the on-board HP "not quite SATA" controller too.
Shame on you HP.