A journalist friend of mine informed me of this. Photos from 2010 of a dogfight with Heineken banners plastered around the venue has recently gone viral on Facebook, with consumers threatening to boycott Heineken products. The photos are from a 2010 dogfight "championship" organized by a pit bull terrier breeders' club at a UB nightclub called Elite. According to the site that originally posted the photos, the breeders' club has been organizing these "official" fights since 1997. (source here. be warned though, graphic images of animal cruelty).

In an official statement on their website, Heineken denies any knowledge of or involvement with this activity, stating:

Images continue to circulate in social media channels showing a dog fight, with Heineken® banners clearly visible in the background. This is very distressing and totally unacceptable. As a company and a brand owner, we do not and would never knowingly support any event, outlet or individual involved in this type of activity...The venue owner has verbally confirmed that Heineken banners are visible in the pictures because the previous evening the club had been decorated for a promotional event and he had failed to remove the banners once it was over. [Source]

The company claims to have removed all promotional materials from the venue and ceased relationship with the nightclub since the incident came to light.

I have not been able to find any information on laws prohibiting such activities and according to friends, dogfights are not illegal, i.e. nobody's bothered to address it so far. These events are most likely low-key and never publicized, as I have never heard of this before yesterday.