I had the question clarified by the client. Yes, it refers to pre-roll campaigns.
After receiving this confirmation, I realized that roll campaigns is a broad term that encompasses
pre-roll campaigns, mid-roll campaigns and also post-roll campaigns (ads displayed before, during and after the video, respectively). And these terms are often left in English.
I'm thinking of translating "Roll Campaigns" to
"Anúncios Pre-, Mid- e Post-roll". What do you think? Any other suggestion?
Some useful links I found:
http://suporteliquid.sambatech.com/entries/20093166-o-que-e-...
http://www.proz.com/kudoz/english_to_portuguese/internet_e_c...