If the amplitude and phase of the vibration were significantly different between OGE and IGE it would be necessary to smooth both conditions. In fact the difference is negligible, and if it isn’t then you have other problems which no amount of pitch link, hub weight, product balance or tab will help. The hover coefficients for the RADS and Chadwick programs for Bell Helicopters are all developed IGE, I can't speak for the Lab.
As for your hoisting question, I vote for the trees. Since we are in the business of risk management, we compare the chance of an engine failure with that of losing good reference. I suspect (hope) the latter would pose the greater risk. Additionally, the shorter hoist distance would also limit the exposure time to an engine failure at a critical moment. Just a thought…….