Some do, some don't. RBL generally only issue one card for most customers, but most are also able to keep their preexisting co-branded Bajaj Supercard too. There are other exceptions like the one person in this thread with three cards.
Their policy may be changed now if they are truly going to partner up with fintechs.
It's a proper CC and shown as CC in the CIBIL. Credit Line is it's feature. You can transfer credit limit to bank account. If you do that, then that transferred amount will be considered as Personal Loan.
Also, Duet card used to be Paisa on Demand card. Not sure if credit line feature is still active.