I'm using employee purchase program link to purchase a new Mac, but don't seem to get any rebate compared to non-employee link. Any ideas?

I suggest that you check with your employer to verify that they have a contract with Apple to provide their employees with a discount. If your employer verifies that you should be getting a discount, have them also verify the link that they are providing you to do so.

Apple do not offer discounts on all their products, for example iPhone hardly ever get corporate discounts. It could be if your looking at buying for example the latest MacBook Pro that because this is so 'new' a model Apple are not yet offering any discounts.

I would however expect the Mac Pro and the iMac to have discounts available being these are older models. (Particularly so in the case of the 'ye olde' Mac Pro.)

You won't be able to get both an employee discount and a rebate offer that is made to non-employees.