I thought I'd add some information on this. I'm currently using Dragon for Mac 5.0.5 running High Sierra, and it works extremely well, and it was for that reason that I came to this post, as I'm thinking of upgrading to Mojave, but was wondering whether I would lose the Dragon functionality!!
Anyway, I have been using a really great bluetooth headset that works well with both Dragon for Mac (on High Sierra) and also with the built-in Mac dictation feature, and that bluetooth headset is the Plantronics Savi W745 Headset...BUTit cost me around $200.00 when I bought it from Walmart online back in March 2016. Today i tried the Mac dictation and I can report that the Mac dictation cannot perform anywhere close to what I'm getting with Dragon for Mac 5.0.5 WITH High Sierra, so I think I'll be staying with High Sierra for awhile!!