MrB,
You can take them both together but as the purpose of the sample is to gauge the effectiveness, doing so would be a bit silly (as Shrek has pointed out).
Rather than waiting until you have finished the Hemo Rage I would take the Pre Workout NT (on a day when you don't take the Hemo Rage), that way you can get a better idea of how well it works in comparison, and you can also compare the value for money - Pre Workout Nt is $69 for 100 serves.
I have to say Pre Workout products are a funny one, personally I am not a fan of DMAA as I find I suffer quite a few sides, anxiety, jittery feelings and it can cause insomnia.
If you do use them, it is always good to take a break for a week or so, and your idea of using it on heavy days only is a good one. CNS overload is no joke, these products shouldn't be used in large doses day in day out, especially the one's that include a "lucky dip" of stims (most of them) where you don't even know how much you are having.