Are my assets safe on Layer 2?

In order to give you the best user experience, Vertex will be built on Arbitrum - an Ethereum L2.
​Arbitrum is an optimistic rollup that improves Ethereum’s scalability, offering faster transactions and lower fees while providing the security of Ethereum. Ethereum’s security comes from it’s consensus method, Proof-of-Stake, where a network of decentralized nodes validate transactions.
Whether or not Ethereum is safe is up to you to determine. Remember to always use best practices while dealing with crypto.