The Atom 0.3 feed generated by the latest WordPress appears to be correct, but the Feed Validator rejects it:
See this sample feed from nothlit.com.
The date in the feed appears as:
While this is consistent with Atom 0.3 and the W3C (http://www.w3.org/TR/NOTE-datetime), you could replace the Zulu notation with the following notation:
This is also compliant and is .NET-friendly. .NET 1.1 DateTime is unable to parse Zulu dates.