" as a bridge for two different subnets"
So your saying he is running 2 different address schemes over the same wire?
" network is such a mess..."
Well why don't you fix it, clearly if he is asking you for hardware suggestions you should be able to provide more ideas on clean up.
It is must better to fix any mis configurations in the network before just throwing hardware that can do what he is currently doing, if what he is doing is a cluster.. Bridging 2 different subnets together seems like a cluster to me - but also missing info, and possible miscommunication to what is actually going on.
But in general no I would not suggest you run 2 different address spaces over the same wire.
eheh kind of expecting to see your opinion here
about the subnets: it's two different companies linked together by this router, in which one of them needs to access the other one resources. And yes, i want to fix it completely but the client just needs this particular problem to be solved right now; if done correctly then the odds of fixing this whole mess are greatly increased (they have a lot of other problems, server wise as well).
Also my issue is... i don't know jack about Cisco routers and no one knows in both companies if that router belongs to them or if it even belongs to the ISPs (them have both).