Could be, I programmed using the low-speed 128 KHz oscillator with that, but not with divide-by-8 set.
I don't know what its limits are, maybe divide 250 by 8.
I was reading the CLKSEL bits the wrong way round.
It is incredibly confusing the way they do that. If you "tick" the box in the fuse calculator, it sets the fuse to 0 (programmed). I think the reason is the default for EEPROM is to be 1 bits, so you "program" them by "setting" them to zero.
So if you uncheck all the boxes on the low fuse side, you get a fuse setting of 0xFF.