I too emailed 2 seperate ad companies just looking to sign up and get an Ad Server URL. Neither responded back. My guess is these channels pay pennies, and myb aren't much worth the time invested in sales/signups/support.
Just wondering is there a reason you don't go with Roku's RAF?
That is weird because then they are lying when they say they fill ads in Spain with their press release, so you should probably reconsider doing business with them. Yume also has an actual office in Mexico - so it's doubly odd they wouldn't have spanish ads.