Ethnics were always in the 500s under Source Cable. I wouldn't read anything into how Source Cable or Rogers Hamilton have their channels setup. Both systems are numbered based on pre-Rogers setup. Also Source Cable has nowhere near the amount of ethnics that Rogers main systems have. Source Cable has maybe 20 ethnics.
I fully expect that Source Cable and Rogers Hamilton will eventually have the same channel numbers as existing Rogers systems.
It could also be technical reasons, maybe some equipment needs to be installed in their Headend which may take time, maybe SDV stuff, who knows.
Possible but Source Cable doesn't do SDV either and the former Shaw system has many MPEG-4 HD channels so that system shouldn't be starving for bandwidth. They could easily offer what is available on Source Cable now without any issue.