Yes, they'll still work, but the installer might not want to set them up to keep working. Here's the problem ....
An HD upgrade means you'll get a Single Wire Multiswitch dish. Those old Tivos are not compatible with the SWM technology. You *could* get a regular non-SWM dish with a SWM16 switch, and use the SWM16's four "legacy outputs" to feed a Zinwell WB616 multiswitch (or whatever multiswitch you used with those 5 HDVR2's). But this is not a standard installation and I doubt the installer will have that equipment, so you would need to do it yourself.
Also, note that activating those old Tivos will still incur a $6/mo "Receiver Fee", regardless of whether or not you own them.
Sony SAT-T60 120GB (v3.5b)
HR20-700, HR20-100, HR21-200 HD DVR
HR10-250 HD DVR 400GB (v6.4a)
H21-200 HD Receiver
R10 DVR 160GB (v6.4a)