Yes and no.
Having one M2 Pro miner allows you to only need HALF of the amount of MXC for maximising your DHX mining, compared to having NO miner when mining DHX. But it only does this for the first one million MXC. A second miner would continue the same benefit past one million MXC (up to two million), that the first miner was providing for the first one million MXC. A third miner would do the same for two million to three million MXC, etc.