Yes, it’s not only fine, it’s very very good. Giving players actual gameplay reasons to participate in content is a good thing. If you want crawgs, you can always come back in late 8.1 or 8.2 when heroic Uldir is a total joke anyone can faceroll.
Yes it means non raiders might not get it, but you know what? That’s just fine. Having interesting rewards in the game that aren’t accessible to everyone is good because (if enough special things like that exist) everyone gets to feel a little special. In a perfect world every type of content would have fun little exclusive things for many classes.