Is there a way to upload questions to "Retrieve and Rank" (R&R) using cURL and have them be visible in the web tool? 
I started testing R&R using web tool (which I find very intuitive). Now, I have started testing the command line interface (CLI) for more efficient uploading of question-and-answer pairs using train.py. However, I would still like to have the questions visible in web tool so that other people can enter the collection and perform training there as well. Is it possible in the present status of R&R?
Sorry, no - there isn't a public supported API for submitting questions for use in the tool. 
(That wouldn't stop you looking to see how the web tool does it and copying that, but I wouldn't encourage that as the auth step alone would make that fairly messy).
Upload questions to Retrieve and Rank using cURL, visible in webtool