It's not using an engine for Web3 integration. Mostly custom solutions based on OpenZeppelin smart contracts and some Thirdweb contracts.

I looked into all 3 though (Thirdweb, Sequence and Moralis). Either one would probably be fine. I'd prefer Thirdweb or Sequence.

You can also go for custom + indexer (i.e. https://ponder.sh/), as this will replace your need for using a thirdparty to get contract data - i.e. NFTs & co.