Interesting thought! "Hopping" between different blockchains could make tax evasion really really easy.
But what would be important to know in order to answer your questions is whether there is something like a marker on both the Bitcoin and the Ethereum blockchain which indicates that there has been an atomic swap. Does someone of the other readers know something on this point?
By the way IMF-economist Kenneth Rogoff seconds your reflection https://www.coindesk.com/ex-imf-economist-kenneth-rogoff-joins-bitcoin-will-collapse-chorus/
RE: Did Charlie Lee And Atomic Swaps Just Make Tax Evasion The Norm In The Crypto World?