Yes SVT-Vp9 and SVT-AV1 are pretty experimental. SVT-HEVC works without the two others fine on my side. I think implementing SVT-HEVC is ok, but with the two others we should wait a while. I have done a lot of encoding and stability tests with SVT-HEVC in voukoder now and everything worked.
Edit: I can upload a Voukoder .prm file with SVT-HEVC included if you want to test some encodings