No it is not on the syllabus and you are allowed to use it. I used the return of the king myself and do advanced and i recommend any of the lord of the rings triology they are great.
I dunno. according to my 3u teacher, they don't like it because the teachers feel like your douple dipping (whatever that means). but it doesn't stop you from doing it .
They're really looking for how well you're able to explain and relate ideas. So if you're choosing similar texts (sequels) you may come across as lazy to a marker. But yeah, they're awesome ^^