Hi Hazel!
I'm in a similar boat. I have an MFA in poetry and was just admitted into a PhD program in literature with a full fellowship. Honestly, I was surprised they took me! I had all sorts of impostor syndrome as I was prepping my application. I hadn't published anything scholarly beyond a handful of academic book reviews.
I've been a lecturer for a good number of years and have a strong background in and understanding of pedagogy, so maybe that helped. I also have a lot of creative publications (two poetry collections, another forthcoming), and in my SOP, I made a case as to how this was connected to the kind of scholarly work I want to do. My area of interest is gender studies, and my poetry is fiercely feminist. I think being able to articulate that connection made a big difference, but who knows.
When I spoke to the grad director on the phone about my offer, she seemed to know a lot about my creative CV, so clearly she looked at it.
I have pretty mediocre GRE scores at best.
I also audited a few lit classes where I teach. I wrote a term paper for one of them and got feedback from a few colleagues, which I used as my writing sample. I don't think it was particularly great, but hey, it worked.
So I think, as a creative writer, if you can articulate and explain how you're best suited for scholarly writing in your SOP, it will make your application competitive. But then again, this is my first year applying and really I felt a little lost the entire time!