Spekter1080
Most scanners and Brute force programs do indeed have options/setting to scan/ bruteforce through a proxy.

I also believe (not sure) that their is a program you can run on the background where you can assign a proxy to it, so that every outgoing data is going through that proxy.


Dominatorx
I dont think you can know if a portscan is coming from a proxy or from an intruder.
Unless you can find the contact info of the proxy, so you can ask the admin of the proxy to check out his logfiles.
If the ip is coming straight from the intruder, you can contact his isp.
A way to find his isp is by using nslookup.

-mlite