The way the sides stack up wholly depends on the game organizer. He's God and his commandments must be obeyed.
You can stack Multicam with the digital side since it's computer generated also. You can stack Auscam and woodland on the same side. You can even mix solid OD and Tan VS. gear with a pattern.
The key is that when god commands the Canadian side defending the Island of Rockravia shall wear CADPAT or OD only and Insurgents fighting to overthrow the oppressive Junta shall wear Black or Civi attire only that's what you wear. You don't sign up as an Insurgent and wear OD. Or show up to play on the CDN side with jeans and a T-shirt.
Some organizers will plant moles in your team who will change dress, or sides. It does happen. Some events can be very scripted. You never know, the organizer might have a four man JTF-2 team on the Canadian side in Civi attire who gets inserted undercover in the mix. The key is that is within the structure of the event.
If you don't agree with a dress requirement you have the option of not attending the event. Just like if you can't abide by not bringing Hi-Caps when there's an ammo or magazine restriction.
If a game organizer specifies some outrageously rare uniform that no one owns the game will either fail because no one will attend or the 4 guys who do own DPCU will crushed by a horde of MJK.
This all goes to the effect of being courteous to the event host and to your fellow players by following the rules.
This is not for Sunday morning hack around skirmish where who cares who's on what side and usually the guy who arrives last gets to be hunted down by the group. On days like that wear what you like.
Airsoft, where nothing is hurt but feelings.