Depends on the franchise and the editorial policy. Generally, continuity between different tie-ins is optional. Star Trek tie-ins have gone through a lot of phases. At first, they had no continuity except in the case of sequels by the same authors. Then a loose inter-novel continuity formed to a degree in the mid- to late '80s. But then that Roddenberry memo happened and Richard Arnold started imposing a zero-continuity policy on the tie-ins -- and even though he was kicked out in '91, the novels didn't really start developing a continuity again until the late '90s, though mainly from 2000 onward. And even so, it's still not mandatory; most books are in the "novelverse" but there have been plenty of exceptions.
Otherwise, I've seen tie-ins that had strong continuity (like Star Wars and the Doctor Who New/Missing Adventures), tie-ins with zero continuity, and everything in between. It's pretty rare for the actual studio to care about anything beyond consistency with canon. Though it's getting more common these days for tie-ins to be consistent with each other and even to be nominally canonical.