Update 3- Using the caption preset for .srt, I was able to export a sidecar caption 608 file for a 24p video. So far it has not been rejected by AVD.
So, to sum up so far- What has worked with Amazon Video Direct Caption requirements exported from Premiere CC.
608 caption files only. Sidecar (of course).
29.97 fps content- .scc
24p content- .srt
Since they are 608, these are basic pop on captions, but the should meet the requirements for content. These are the only file types I could get to work, at this point. I am still waiting hear back from AVD support on why 708 captions/file types are being rejected.