That's what I assumed, but the datasheet I looked at showed a daughterboard marked "EV-LTZ1000-REFZ". At any rate, very satisfactory for my needs and wants. So after I bring up my VNWA, Bodnar GPSDO, Zybo, MicroZed, LimeSDR and BeagleBoard X15 I'll get one. Right now I am in "missing part" purgatory.
Edit: I went back and looked at the datasheet from Digikey and the LTZ1000 is on a daughterboard with no place for it on the AD5791 eval board. i don't know if the unpopulated daughter board is part of the AD5791 eval board or a separate item. i've not yet fund a source for the LTZ1000 board.