Agreed, we are as well 
VLAN, VRF, whatever.
+ optimal tweaks include local flow proxy that can also rate
limit / re-sample, and send topk talkers over 'true' OOB.
Avi Freedman
CEO, Kentik
avi at kentik dot com
Yes, a lot of distributed flow collection/analysis architectures are deployed this way, doing more than top-talkers, even. The key is that traffic between the elements of those types of deployments *must* not be disrupted; true OOB is preferred, but VLAN/VRF is still the norm, there.