No, it's not absolutely necessary as far as the ERAS system. But for all practical purposes, Why do you want to apply without uploading your USMLE transcript?
No program will ever consider seeing your application without looking at your USMLE transcript.
If you mean by your question that should you apply before the ERAS system successfully transfer it after your request. Then the answer yes you can but I prefer until it's transferred which takes 2-3 business days.