The spectro embedded in the HP "z" series printers is essentially an iSis. I got into a mild argument the other day with a colleague that claims it's EXACTLY like an EyeOne under the hood (it's not). Of course, they call it "i1 Color by XRite" or whatever but it's more like an iSis than an EyeOne, with the LED illumination being the key element tying it to the iSis. Because of this, it's natural behavior is that of a UVcut-filtered spectro since the LED illumination gives off no UV. As a result, I assume you'd find fairly big differences between it and an unfiltered Spectrolino, especially with certain papers. The more OBAs present in a media, the larger the difference.
the HP "z" printers maybe aren't the hot ticket for fine art printing compared to Epsons, especially the x900 Epsons, but they make fine proofing printers when driven with a RIP (GMG, EFI XF, etc.) that supports the embedded spectro for fully automated calibration. I think they're nice machines, all things considered, and find them to have more consistent behavior than most Epson printers I've used.