My dissertation advisor & Chair was professor A. He all of a sudden was severely ill and left the program right before I proposed my dissertation study. I built the study under his supervision, including part of the data analysis, but he didn't have a chance to read even the first draft of the proposal.
Professor B (from my department) took over as the committee chair. The dissertation was not exactly her area of specialty. She served as the chair (someone needs to and the department decided that she would take the role) and arranged the defense by signing off on paperwork and making sure the procedure functioned. Her advising role did not involve major, valuable feedback. She's acting like any other committee member by asking a few questions and checking the final revision.
I thanked both advisors in the acknowledgment.
Would thanking professor A in the dedication be too much? I frequently see people thank families and friends but advisors/professors are always in the acknowledgment. Also, this might make professor B feel bad if she sees the dedication.