Is it possible for a Property checkpoint to validate against a variable?

Yes, it can.  When running through the wizard, you don't have an option for using variables at that point.  However, once the property checkpoint is added, if you click into the value field, you'll get an ellipses button

When you click on that, you'll get an edit form that will allow you to edit and adjust all the parameters for the property checkpoint, including the value field.

Give this a try and see if it works.