The concept of an atomic swap is not a part of the lightning network.

It's just a structure of transactions utilizing hashed timelock contracts (HTLCs) in order to achieve a trustless exchange of different currencies on different chains. Until now multiple atomic swaps were made on bitcoin.
ATM I'm writing a thesis about atomic swaps and how to recognize them. There are a few different scripts for HTLCs, but they all do the same thing: they lock value for a specific time, except the counterparty can provide the preimage of the given hash.

One implementation of an HTLC looks like this:

In order to have an atomic swap you just need an implementation which achieves the same thing. In ethereum you could also write a smart contract which does the same. As far as both parties can watch the blockchain and what is happening there, it is possible to make an atomic swap.