Does Mathematica support importing ISO 8601 date strings?

You can use JLink (as already mentioned while I read JavaDoc). Searching StackOverflow brings up this highly voted answer

Converting ISO8601-compliant String to java.util.Date

I don't know whether it covers the whole standard but this works out of the box. If this is not sufficient, you can use an equivalent piece of code written for Joda Time

Needs["JLink`"]

ParseDateString[date_String] := JavaBlock[
  InstallJava[];
  LoadJavaClass["javax.xml.bind.DatatypeConverter", 
   StaticsVisible -> True];
  DateList[
   javax`xml`bind`DatatypeConverter`parseDateTime[date]@getTime[]@toString[]
  ]
]

This uses the DataypeConverter class which is available without in standard Java 6. It converts it into a standard date string which can then be used with DateList.

ParseDateString["2010-01-01T12:00:00Z"]

(* {2010, 1, 1, 13, 0, 0.} *)

As of Mathematica 10.2, DateString and DateObject support this format directly. For example:

In[1]:= DateObject["2015-09-17T03:12:44"]
Out[1]= DateObject[{2015, 9, 17}, TimeObject[{3, 12, 44.}, TimeZone -> -4.],
         TimeZone -> -4.]

Use Joda Time with JLink. Joda is fully 8601-compliant, and with JLink the whole Java universe is immediately at your fingertips from M.

I've posted a few replies in this forum using Joda Time, for example Faster alternatives for DayOfWeek

where I've mentioned that Joda Time is fully 8601-compliant.