More faithful sequels to the movie can be found here at dA. Thankfully, this one isn't canon to the movie in any way for at least 5 reasons.
1: Don Bluth wasn't the director.
2: Continuity errors; Nicodemus didn't prophesize the events in the first movie.
3: This is inferior to the real movie, and book for that matter.
4: The book already has a sequel, which this movie didn't follow.
5: THE FIRST MOVIE WASN'T A FUCKING MUSICAL! It only had one song that wasn't nearly as bad as the songs in the sequel.
Besides, it's a "sequel." what did you expect?
If it weren't for all that, I'd have to accept it as canon. So in your face, MGM! It's not a Secret of NIMH movie. It's not official.