Can't tell you about the roid cycle, but here's some HMB studies that show mixed results with non-roid using athletes. It's not the cheapest supplement so make it a lower priority... but the good news is that they also show that HMB has no side effects
HMB and creatine have been shown in studies to produce more results than either supplement used alone. Over here in the UK, the biggest selling creatine product is cyclone by maximuscle - its a creatine/HMB product and it works wonders.
To answer your question about the cycle, im not sure it would enhance the drugs but any amino acid or protein based product will enhance the muscle building process.
The good news about HMB is that it actually seems to work! I was doing it along with my AAS but ran out and didnt wanna shell out another $50 for another bottle. While I was natural I did a bottle and im convinced it helped.