I think you can, if they're working outside with their eyes open (i.e. their own due diligence complete as well as PSB onboard, by definition) or working inside with a rate increase. Those people are in a better position than many numpties in the private sector that are completely clueless about IR35 and operate as BAU, BoS, permies. Stupidity doesn't discriminate between the PS and private sector, unfortunately.
Absolutely. Does anyone really think HMRC is going to pursue someone who is working outside, the PSB is onboard, and any version of the ESS ruled them outside?