Thales smart contracts support sUSD as collateral to mint options. sUSD is the flagship stablecoin of the Synthetix, a decentralized derivatives liquidity protocol.
There are many ways to get sUSD, all are equally suitable for the purposes of using Thales smart contracts.
sUSD, an ERC20 token, is the only truly decentralized stablecoin that has demonstrated an ability to hold a peg against other popular stablecoins including USDC, USDT and DAI, primarily thanks to the Curve pool linked above.
sUSD is completely censorship resistant. There's no way to stop one person from sending another person sUSD.
Similarly, there's no way to stop a person from minting sLONG and sSHORT options tokens with sUSD. In the event of a front-end not being functional for whatever reason, a user could always interact with the Thales smart contracts directly through a blockchain explorer like Etherscan.