Rootstock is **not** a Bitcoin sidechain as per the sidechains whitepaper. It does **not** benefit from Bitcoin hashrate.
That is the definition of a sidechain, a separate chain that has its own mining
RSK is a Bitcoin sidechain, so it has its own network, and its own blockchain, but not its own token.
A sidechain.borrows all coins from its host chain. So while it can not have its own block *subsidy*, it still has miners earning transaction fees.