Hematite is a very powerful stone that contains iron ore - whereas malachite contains copper ore. Iron, the metal of Mars can indeed complement copper, the metal of Venus - just make sure that the necklace is well balanced between the two, or contains more of what you actually need.
If you want to use the necklace to bring up suppressed emotion, then hematite can help you face the more difficult ones; but it can also make you less aware of the subtle ones, so it depends what you are looking for. If one of the suppressed emotions the malachite brings up is anger, then hematite can intensify it - but at the same time, will make you stronger to deal with it. Traditionally, on top of its physical use in staunching and purifying blood, hematite is used for protection and by professionals who have to listen to a lot of people's problems, like doctors, psychologists, lawyers, etc., in order to help them listen more effectively while protecting themselves from the negativity and allowing them to speak with authority.
It's fine to wear Malachite every day and even sleep with it (it helps for a peaceful sleep!) - just cleanse and recharge it regularly.