[benchaney]

You cannot write a tumbler as a smart construct, so no.

[sillysaurus3]

I don't see why not. The bitcoins would just need to be converted to ETH first, which I think can be done anonymously.

[benchaney]

The execution of all smart contracts is deterministic and publicly verifiable. It would be trivial to find out how much money was sent to each participant and why.