Here is a video from the recent BUILD conference that shows a Qualcomm based Windows 8 ARM table running Adobe Flash within Internet Explorer (Desktop). This confirms that even the ARM based version of Windows 8 tables will be able to run non-metro third party browser plug-ins (and presumably applications).
After all the recent articles about the iPad promo video showing it having flash support Apple has done a 180 and has now removed the flash content from the video on their website. This shows that Apple video of the device was a total mock up and that that it is highly un-likely that it will get flash support. Seeing that web plug-ins like could be used to write fully functional apps (thus bypassing the AppStore) I seriously doubt that Apple would ever let SilverLight and/or flash run on their device.
There has been a few posts about some of the videos that Apple released showing flash content being rendered on the display. However this seem to be Apple have a marketing stuff up as another pages that shows the Safari displaying the New York Time home page with the flash based video clearly missing. I speculate that the video shown on the Apple web of the iPad was a mock up of the device using the Safari video captured on OSX.