I didn't say anything about his bosses having any prior knowledge, where did you get that from?
When, before this update, did Sandra ever prove that she was any wiser than them? Also, Haley knows Sandra on a personal level, where Haley doesn't really seem to be as personal with her bosses, not like MC is. That may be why he chose to confide in them instead. I can understand him going that route. Also, Sandra wasn't exactly around, she's most of the time in another place with her new promotion, probably another reason why he chose to not confide in Sandra about it.
EDIT: Of course! Just realized this, but this is how Haley and Sandra build their relationship and become more intimate with each other. This is Haley's path into the 3-way with Sandra and MC. Pure genius.