There is no inheritance in resource dictionaries, only replacements. Resource dictionary is completely flat structure. When created merged dictionaries goes first in order they are declared. Dictionaries declared later on the list have access to things declared in dictionaries that goes before them. They can also replace that things. Things declared at dictionary level have access (and may replace) things declared in merged dictionaries.

So you can reference things from merged dictionaries, but in opossed way you were thinking.