During the suspension period the employer employee relationship remains and in the absence of any express order saying that the employee placed under suspension pending enquiry is not entitled to any increment, he should be paid increment due and the subsistence allowance should be paid based on the increased salary. Obviously, subsistence allowance is a percentage (50%, 75% or 100%, as the case may be) of his pay and once his pay is increased by the element of increment given, the subsistence pay will also increase.
No doubt, if your increments are purely based on performance, you need not pay it. But if the employee is under a time scale with annual increments marked against each grade, he should be paid the increment.
In support of the above there are a lot of court cases available. One case is attached for your reference.