Is it legal in skirmish when an attack is declared against a force user to play both camoflauge and deflection effectively applying -4 accuracy to the attack?

Yes you can. However, you can't use the same trigger to use multiple copies of the same card.

So for example you can't use two Deflection cards against the same attack.

Similarly you can't use two Jungland Terrors in the same end of round phase and you can't use two Reinforcements in the same start of round phase.

Cool. Thank you.