"blues musicians playing odd instruments"
Hey, I resemble that remark! I play a crazy kind of washboard/soundeffects gizmo. I call it my 1929 Maytag Custom Special Dixie Delta Deluxe Eldorado Rhythm Board (MCSDDDERB pronounced micksderb). I don't play it regularly much these days as I'm not involved with a suitable combo, but I still update it with as many weird or odd acoutrements as I can. It's very much a work in progress. I would say that it takes a special kind of combo to want to add such an unusual array of pre-cussion and sound effects to the mix.
I've played in a variety of combos that focus on blues music. It wasn't the variety of blues that you hear most electric "blues" bands playing today. The groups I've been involved with were all leaning heavily toward acoustic instrumentation. I guess you might term what we were doing as a form of jug band style blues though I don't think we fit neatly into the contemporary definition of that category either.
I also play the musical saw, another very unusual musical instrument, and not one that is widely accepted by any formal musical genre. I have, however, and sometimes still do, play blues with my saw. I've always thought that the spooky nature of the sound produced by the saw could easily lend itself to blues and ballads.
My fascination with these two instruments has left me in the position of being somewhat of a musical outsider in this neck o' th' woods. Primarily, I'm a guitarist, but I've even bent the rules some in this pursuit by managing to create my own resophonic guitar out of junk I found at garage sales. I play my square necked creation bottleneck style with a rather large slide, a frictionless marine propellershaft bearing, or as it's called, a cutless bearing.
As a result of all of this interest in odd instrumentation, I mostly gig alone. On those rare occasions when I am able to pick up some help for a show, I really enjoy having a friend join me on keyboards, piano, accordions, and yes, he's also a great melodica player. I don't think you can limit the blues by instrumentation, but Steve Martin used to joke about the difficulty of feeling blue while playing bluegrass style banjo. ;o)