Is it possible to complete the main question without joining either the Stormcloaks and Imperials?

I don't remember very well, though do recall that the dialog options when talking to Tullius and Ulfric made it so you HAD to first join their side before they'd talk about anything else. Am hoping there is some way around that, that I just wasn't aware of.

yes

thats usually how I do it. pick a side at the meeting and then after the MQ I'll officially join up.

both sides will require you progress past the initial dialog resulting in Tullius or Ulfric telling to talk to Rikke or Galmar. Don't talk to them. instead try and talk to Tullius and Ulfric again and they will have the dialog for the meeting

So as long as I don't talk to Rikke or Galmar my character wouldn't be considered as having joined a side? Just to reconfirm that I am understanding you right.