Generally speaking none of the Star Trek books are considered to officially be canon. The only material considered 100% canon to Star Trek are the television series (except the Animated Series) and the feature films, though there have been many statements acknowledging that it is fluid and no one has a definitive answer to what is truly Star Trek. In a post from 2003 on the official Star Trek web site they outright stated:
As a rule of thumb, the events that take place within the live-action
episodes and movies are canon, or official Star Trek facts. Story
lines, characters, events, stardates, etc. that take place within the
fictional novels, video games, the Animated Series, and the various
comic lines have traditionally not been considered part of the canon.
But canon is not something set in stone; even events in some of the
movies have been called into question as to whether they should be
considered canon! Ultimately, the fans, the writers and the producers
may all differ on what is considered canon and the very idea of what
is canon has become more fluid, especially as there isn't a single
voice or arbiter to decide. Star Trek creator Gene Roddenberry was
accustomed to making statements about canon, but even he was known to
change his mind.
