From discord:

Hey, I was having difficulty setting the harvest level of ore dictionary entries and I noticed that those entries are actually being parsed and processed before mods like IE and Mekanism are adding their ores
It might be a bug with Underground Biomes, but, I'm seeing log messages for my attempts to override oreTin, oreCopper and oreOsmium
I can override the individual blocks just fine, just not the oredict entries
To be clear, the native ores don't register either with the oredict, not just the ub provided ones

I see, so overwriting the block can be my workaround for now I presume. I will go this route for now then.
God bless this is gonna take forever lol.

Should be fixed in upcoming version 1.6.6