Updated 1 July 20122013: Re-awarded MVP in Excel which was based fully on SO contributions:)
I think the answer as to whether Stack Overflow participation would be considered for a MVP award/re-award is certainly yes. The issue would be more about the where the level of participation (based on question traffic in the MVP tags) would be sufficient.
I have been awarded as an MVP for Excel in 2010 and 2011, based mainly on my contributions at Experts-Exchange in Excel. These days I am spending most of my Q&A time at Stack Overflow & Super User while maintaining my longer articles at Experts-Exchange. I think these efforts are comparable to my past two years and I certainly hope that this keeps me in the frame to be re-awarded.
There was a noticeable broadening of the scope for community participation that helped qualify for a MVP award around 2006/2007. This has led to around 300 or so MVPs at Experts-Exchange (at least 8 active ones in Excel). Part of the assessment change was clearly driven by the much higher traffic at these forums - the growth in questions in the Excel space at Experts-Exchange from 2002/03 to 2007/08 was truly remarkable.
The traffic at Stack Overflow and Super User in the excel tag is less than other forums (which speaks to my initial point about level of participation) which is a potential disadvantage. Countering this, I think that the Stack Overflow forum design more clearly recognises expertise from the community than question asker perspective. There is also a significantly greater focus on collaboration and answer quality here compared to "winner takes all" forums where the focus is on chewing through questions as quickly as possible to accumulate status.
I will check in with my MVP lead and post an update if I am off the mark here.