It is not currently possible to constrain the value of a slider to an integer. It's a great suggestion for a future enhancement, and I'll make sure it gets added to our database of enhancement requests.
In the meantime, I have an idea for a workaround that would allow you to use sliders while still constraining a parameter value to an integer. Let's say that the parameter you want to modify is named kInteger. You can add a new parameter (let's assume it's named kContinuous) that you control by your slider. But then you also add an initial assignment rule kInteger = round(kContinuous) to round the selected value to an integer.