I had an email exchange with Blackspire about this when I was looking for a 52mm chainline boost ring and they told me that using a smaller than 55mm chainline on a Shimano crank was impossible. They said "The 55mm chainline with those cranks is designed to work with 148mm boost rear axles. We have this printed on a sheet directly from shimano. If you are considering that you are needing a different chainline you may want to consult with Shimano directly or a local bike shop with someone who can see your bike hands on and see what they say."
I'm pretty sure that if the frame clearance is sufficient, it's entirely possible to use a 52mm chainline ring on a Shimano boost crankset. Maybe they won't advise it for liability issues if it doesn't work, but like other have mentioned, it's possible to make it work. I did not have issues with the 55mm chainline, but seeing the chain angle, it must wear out the bigger part of the cassette and chain much faster (which is the part I'm using the most). My One Up guide is installed pretty far outboard too and I don't see having the ring 3mm inboard causing any issues.