Yes, you can claim for any difference between your service pay and earnings from your business up to a cap.
You are also entitled to claim as an an employer, if you needed to recruit someone to replace your role in your business while you are mobilised for example. This is also subject to a cap. When you return from mobilisation, if skills you need to be able to return to your role have lapsed as a result of your mobilisation, you may be able to claim for the cost of re-training.