Is there any way to prevent certain sub forums (outside of group permission) from showing up in the Activity Stream? We have a few paid sub forums for vendors but would prefer their content not show up in the activity stream if at all possible. 

You can create a custom default stream that doesn't include those forums. Would that meet your needs? Your members will still be able to create their own streams to see them if they wanted to.

1 hour ago, eGullet said:

You can create a custom default stream that doesn't include those forums. Would that meet your needs? Your members will still be able to create their own streams to see them if they wanted to.

I was hoping to do this by default while I don't personal care, apparently some of the members feel it's too much work to create their own custom streams. (One it seems, can never make "the members" happy) 

You have control over your board's default stream, you can make it include whatever forums you want.

2 hours ago, eGullet said:

You have control over your board's default stream, you can make it include whatever forums you want.

Great! I searched around the admin panel but can't seem to locate where the controls for this are

In System->Streams, click "Create new," create your stream of choice, and choose  the "Default Stream" option at the end.