From briefly having worked on a project where this was a relevant issue, and I had to throw good people of foreign nationality off the team due to higher up NASA decisions: ITAR also becomes relevant when you want to access data and hardware that is ITAR regulated for use in your mission. This is the case for all space missions – even for SpaceX, who likes to do things in-house – since the advanced electronics, alloys, etc. will come from elsewhere and fall under regulation.