HARM has double of the length, compared to the RS-2US missile acting as firing range target in Ustka.
Yes, but the HARMs are presenting minimum-ish cross section to seeker and fuze when launched at a SAM. I also suspect the test shots may carry a radar reflector, at least where old systems are involved.
What is more interesting...
...with the S-300PS system the recommendation is to engage the HARM, instead switching off the 18 channel emitter.
So can PATRIOT, and could do this in GF1. It took hours and hours to verify this information, it came from the investigation of the friendly fire incidents. It also contained information regarding PATRIOT ABM performance.
Later, a PATRIOT got nailed with a HARM because it sang the wrong tune at an F-16.
All in all, I'm not sure that shooting ARMs is a high value proposition, though it's better than sitting there and taking it.