Calling the shots
Review the story board and shot list
Similar to how you should prepare for your own shoot, knowing the traditional team’s shot list will give you a chance to suggest alternate takes for the online version. This may enable you to leverage their existing assets: if you can use set design and talent that's already there, you'll get more value for your budget.
Get a specific budget and shot allocation
If the offline group agrees to give you time at the shoot, get it in writing.
If you're splitting the budget, then this should be automatic, but if you're there by casual invitation and you don’t have an agreed-upon shot list, you're leaving too many things to chance. If the shoot gets behind schedule -- which is often the case -- your shots will be the first to get axed.
Get a shot list, and get it signed.