I don't believe that hydrated lime is hydraulic unless some sort of pozzolan is mixed in. despite my best attempts, though, I'm still an amateur concerning lime.
I think your mixture would work to preserve your beehive's
wood. that's not the only consideration, though. you also need to decide how vapor permeable you want the wood to be. a small amount of linseed oil probably won't totally prevent the wood from breathing, but I would personally be a little wary of using too much oil in our rather damp climate. limewash without any binder
should breath just fine, and if you're not too rough about it, reapplication of anything non-toxic shouldn't bother the
bees much. doing it when they're dormant would probably be the best bet.
I should mention that plenty of folks believe condensation in a hive can be beneficial, in which case oil would be great.
when I finish up the hives I'm working on, one will get a limewash.