Hey there Boogie,

Speaking from experience, I can say they do work, but maybe not in the way you would expect. First of all, I'd encourage you to check you have the correct plugins (eg make only moons spawn and check that indeed they're the only ones to spawn). Secondly, the way I think galaxy generation works is :

-Take a planet

-Roll a dice to decide IF a or some anomalies should spawn (max of 2, including resource deposits for GUI reasons)

-Roll a dice to decide which anomaly(ies) will spawn by using the probabilities

-THEN Make a check to see if the predicate for the anomaly(ies) selected is true (for example, if the anomaly selected has the tag "not on hot" and the planet is lava, it'll just skip).
-Repeat process for next planet

The thing is, in the end, it won't follow the exact probabilities set in weight table, because some anomalies are just way more restrictive than others.

I haven't looked at the hard code to make sure of it, but this is what my reverse engineering taught me, if MonAmiral or anyone who worked on GalaxyGen passes by, they'll probably confirm/disconfirm, but I hope it helps.