It's usually perfectly reasonable, but not really optimal. In this job market requiring React seems worse than hiring someone that is a good frontend developer

It's usually perfectly reasonable, but not really optimal. In this job market requiring React seems worse than hiring someone that is a good frontend developer and has the wits and eagerness to pick up React and whatever tools the team uses, and the job requires. This has the advantage that when - inevitably - tool1 gets deprecated and tool2 arrives you'll have someone that can adapt and learn, and likely you'll also have someone who can teach.