Is there any way to tell if there is a miner (in a pool) on the network, from a network perspective? I'm thinking traffic analysis, packet inspection, IP.

How would that be differenciable from other traffic patterns?

How active do admins look for such patterns?(I'm thinking more P2P stuff)
Pool miners connect to the pool server, not to the P2P network. You may be able to find the pool server by tracing the origin of the blocks, but you can't find the individual pooled miners on the network, as they're not actually on the network.