I don't know what to tell you guys other then "if the USB sticks aren't lighting up, it's not a StickMount problem".
EDIT: interestingly, somebody has just posted the following comment on my DSLR Controller app, which also uses USB host:
Rooted Galaxy Nexus I was originally disappointed upon getting my Galaxy Nexus, as I couldn't get it to work correctly using the Motorola Xoom OTG cable. I saw that people were getting it to work on the nexus, so I tried a different $3 cable I got off eBay, and it works great. Live view to the Nexus screen is beautiful. Should be a fun app!
This implies the Xoom OTG cable may not be compatible with the Galaxy Nexus... which is weird. It's also not the first time I've read similar comments, tbh.