Just make sure you correctly set the MyFamily option in torrc, otherwise a client could (unlikely but possibly) use both of your instances in the same circuit.
Clients also check to see if the IP addresses of the nodes in a circuit are on different /16s.
(But it's still good to set MyFamily so it's clear which relays are controlled by the same person.)
Tim
Tim Wilson-Brown (teor)
teor2345 at gmail dot com PGP 968F094B
teor at blah dot im OTR CAD08081 9755866D 89E2A06F E3558B7F B5A9D14F