My only concern (possibly unfounded) of using engine oil for daily-use fuel is, the additives. Apecifically, the ones added to make the oil resistant to burning. I've heard (my wife is young, so it can't be her tale), it causes a substantial amount of gunky build-up over time. Are you concerned about this issue, CMX?
I wouldn't hesitate a second to burn it in my '91 IDI if I were short of fuel pennies, or all the way up to SHTF. Hell, that's why I bought the truck I did!! I use outboard 2-stroke to supplement my fuel, and add a little lubricity to the acetone-smelling crap they're peddling as diesel nowadays...