I think another thing to think about is the nominal voltage of the cell. An alkaline is about 1.5V and a nimh around 1.2V. This difference becomes even more apparent with cells in series so say 4x1.5 gives 6V and 4x1.2 only 4.8V. I guess how this affects matters depends on the design of the item and I'm not sure pre rechargeable era devices would take the lower voltages into account???

That said we have a digital camera (Pentax K200D DSLR) which, these days, will only work and give a reasonable run with a different non rechargeable AA. I've only seen these Lithium ones in Energizer brand