ATIS wind is usually MAG!
To the best of my knowledge ATIS wind is always reported in degrees magnetic as that's what runway headings are based on.
As an aside though.... just for information... on the good old Airbus, if you stick a wind on the PERF APPR page (the box assumes this figure is MAG) you can check this because after having done this if you then select the DESCENT WINDS from the F-PLN page you'll see the GRND level wind now displayed as a TRUE wind with the appropriate VARIATION correction removed. (Similar deal here if you were to insert the TRUE GRND level wind, the box will apply VARIATION and display the MAG wind in the PERF APPR page)
Cheers!