All hash keys are scalars. And all arrays are arrays of scalars (multi-dimensional arrays have a degree of indirection behind the scenes).

Looking at perldoc -f keys, you get the following:

keys HASH
Returns a list consisting of all the keys of the named hash. (In scalar context, returns the number of keys.)

So in summary, of course you can split a hash key, and do everything else with it than you can a scalar.