While the report should be classed as a rumour (or whisper if you prefer), it is fair to point out that these dates would match expectations and tie in with Windows Phone acknowledged yearly launch cycle, and the RTM and GA dates for both Windows Phone 7 and Windows Phone 7.5. For example, HTC announced its Windows Phone 7.5 devices (HTC TITAN and HTC Radar) on September 1st and the first Windows Phone 7.5 (Mango) devices were available to consumers in late October, with mass market shipments starting in November 2011.
However, at this point in time, there is no official confirmation from Microsoft, or any of the Windows Phone device manufacturers on dates for Windows Phone 8.
With that said, we can reasonably expect to see the first Windows Phone 8 devices announced in Septmeber (most likely from the Windows Phone 8 launch partners: Nokia, HTC, Samsung, Huawei) and the first Windows Phone 8 devices to start hitting the shelves in late October, or early November.
Windows Phone 8 Start Screen
It is worth bearing in mind that availability dates for mobile devices tend to be fuzzy. While launch dates are usually fixed, with devices announced on a specific date, typically at a dedicated launch event, or at a press event co-located with a major trade show (e.g. MWC, CES, CTIA). However, device availability to consumers tends to take place over a period of time, rather than a specific date. This is usually due to a combination of inventory/distribution management and operator/retailer partnership agreements.
For example, in the case of Nokia, it is likely that it will want to launch its Windows Phone 8 devices concurrently in its key US, European and Asian markets (USA, UK, Germany, China, India and so on), but the exact launch dates in each country will be dictated by operator partnerships and inventory availability. Moreover there are likely to be multiple models, each targeted at different segments, and, potentially, different operators.