Audax bikes are just what used to be called fast tourers. generally now, they have dual pivot brakes rather than cantilevers, but that shouldn't make much difference. I suppose they aren't designed to be as stable under load as a full tourer, but I reckon most would be good for a couple of panniers, saddlebag, tent and barbag, if not front panniers.
I'd use an audax bike for touring, without hesitation.