Indeed the piston-fraction doesn't seem to be affected that much: several (g/a) props were still flying today, though imo not as many as on a usual sunny saturday.
The question would be: does an a/c pistonengine have an airfilter like all cars have? I'd guess so... Only problem could be the pitot-tube then. And as stated in our lokal newspaper, the cloud manly affects heights above 6000 ft (or was it meters? And again confuzzlement about metric/imperial system). So low 'n slow should be perfect today - don't forget to entertain the flight controllers as they might be bored...
Yep...
Piston Prop Aero engines do contain Air Filters on the air intake to their Carburettors, like motor cars, etc, and are easily cleaned/replaced.
I would have thought that the Volcano dust would not have affected the Air Filters (clogging-up) any more seriously than Dust Storms, Sand Storms, etc, down nearer ground level.
Paul...Cessna 150....for Hire....Reasonable rates...(Air Filters extra)...

...!
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.