No, as far as we know, Ethereum transactions cannot be reversed.
The DAO hack exploited a badly coded smart contract.
The smart contract runs on top of Ethereum, so there are two layers involved here: the Ethereum blockchain and virtual machine (EVM) and the smart contracts which run on the EVM.
Neither the EVM or the Ethereum blockchain were exploited. That one particular smart contract was.
You may be referring to the 2016 Ethereum fork. That was, indeed, a controversial fork which led to a discussion about Ethereum governance.
In that particular situation, the Ethereum developers did reverse the DAO theft by reorganizing the blockchain. This was done deliberately by the developers. Ethereum wasn't hacked and transactions still can't be reversed, but in that occasion the developers themselves did fork Ethereum to save the DAO funds. They won't do this for any reason though, in fact that fork had widespread support from the community, so your coins are safe. Ethereum won't reverse transactions to harm investors and hopefully another DAO-style hack won't happen in the future.