"the only melodeon player i've ever seen in a duo context leading the singing"?

OK the "I've ever seen" bit is a get-out, but what about:

John Kirkpatrick and Sue Harris
John K and Martin Carthy
John K and pretty much anyone
Pete and Chris Coe
Colin and Karen Cater
I'm fairly sure Roger Watson's worked in some duos over the years

and that's just for starters

Extending it beyond duos, besides the above there's John Jones with the Oysters, Keith Hancock (and me) with the Electropathics...

PS this isn't intended to denigrate Hazel Askew, by the way, simply to point out that it's not unusual for a melodeon player to lead the singing.