No. First of all there is not enough BTC out there for everyone. They will hold the fiat and can hedge with options and futures while they work the OTC desk.
Discussion
Afaik it must be backed 1:1
Yes, and this is actually regulated by the SEC unlike shitcoin βexchangesβ that we are used to. 1:1 is required.
Customer gives issuer cash, issuer gives customer their shares and the cash to coinbase, coinbase puts bitcoin equivalent in the issuers account/wallet with them.