Well, setting the flag YouTubePlayer.FULLSCREEN_FLAG_CONTROL_ORIENTATION after initialization seems to solve the problem =)
...
@Override
public void onInitializationSuccess(Provider arg0, YouTubePlayer arg1, boolean arg2) {
youtubePlayer = arg1;
youtubePlayer.setFullscreenControlFlags(YouTubePlayer.FULLSCREEN_FLAG_CONTROL_ORIENTATION);
arg1.loadVideo(campaign.getVideos().get(Integer.parseInt(v.getTag().toString())));
...