Thank you for this answer lovebugfarm; it's very insightful!
To the OP:
I smoke marijuana regularly, for me it is a medicinal thing; I am a combat veteran and smoking pot helps when things get "hazy." That being said this could be a very expensive experiment, so here's my 2 cents on this subject... I don't think you could get your roaches passed the odor of the flower. Marijuana usually had a pretty distinct "skunky" smell that is generally not appetizing to anybody. I have never witnessed a person smell a marijuana plant and have an appetite flare... they want to smoke it then the hunger follows

Also these days plants are being grown with such concentration that a single plant could smell up the entire house; I almost feel like the smell would repel the roaches and you would have to trick them into eating it.
If they do eat the marijuana I'd be careful feeding them to other animals... I have not heard of a human overdosing from THC but I know that it can be toxic to dogs and cats in moderate doses; I'm unsure of any effect it would have on a reptile or other invertebrate. There are many studies on the benefits of THC on humans and even large animals, but to my understanding these are medicinal in nature aimed at treat a symptom opposed to the effects of a diet change.