>>538202064
Sonic generations also did this. There's precedence.
Silver, despite being from an unpopular game that did not sell well, was included as a major story required boss fight.
There is a page on him in the glossary that catches the audience up to speed. As well as for other characters like Tails, Amy, and so on.

A character not appearing in a long time is not necessarily a barrier to entry for them appearing in a new story as long as it presents them well.