Yeah, you will be able to use them as Tropixxx said, but you'll not get the quality out of the 8mm as you would the Hi8.

Really, Hi8 is just a super duper version of 8mm. So it's all compatible and what not, but things just won't look as good on the regular 8mm as they would the Hi8.

I'd say that despite the good deal they got, might as well take them back to WalMart if you can. You already have the hi8 camera and, therefore, the capacity to film high quality images and so stick with that as you'll get better quality material out of it that will do better to transfer to whatever medium you choose to deliver them through (varying resolutions from a webpage, DVD, etc etc etc)