Yes. Some parameters will not change correctly. The way some procedural maps are handled, is that the tile value changes instead of the size value. So if a cm procedural with tile value 1 is merged into a meter file, then tile is changed to 100. IIRC this is limited to 3 digits, and therefore you might get problems when merging mm files into meter.
My comment above was regarding the real world UVW, but there are specific values that doesn't change correct, like "round edges". When correcting these values, it's worth noting, that all you need to do is tapping in the original unit-name, and Max will convert the value itself. F.x.: If your original value was set set to 1mm and comes in as 1m, then replace "m" with "mm" and the value is automatically changed to 0,001m.
Hope it helps