Blackhole 5 is primarily to dimisnh cabinet resonance and, thus, is more beneficial with lower frequency content. Since the HT1's play full-range, it is more important than in the mid/tweeter section of the HT3's.
If you would like to try an experiment, I can certainly cut some and send it to you. You could then do one cabinet and see if there is any significant improvement.
That said, I wouldn't expect much of a difference.