Is it possible to have a routed path (several Layer-3 hops) between a wccp router and a cache engine ? As far as I remember, a GRE tunnel is established between the router and the cache, right ?
Yes, when you use GRE, you can be serveral L3 hops away, however, increasing latency will reduce performance. You also want to prevent accidental re-interception of your egress traffic.
Hope that helps,