We are planning to rollout Middle Tier servers to 3 remote sites which in
turn have small satelite centres connected over WAN links, we are planning
to have no Novell Client deployed to any workstations.

In an effort to minimise traffic back to the central site we're looking to
place eDirectory replicas at the 3 remote sites for the Middle Tier
servers to communicate with directly.

My question is, Would these Middle Tier servers be suitable for holding
the eDirectory replicas also, or should we deploy either a NW or 2k3 box
just to hold an eDir replica?

The MT servers will only be W2K3 member servers running MT exclusively -
nothing else.