Is there a way to access hard drives while computer sleeps?
Sure.  It all depends on the architecture of the machine.  For instance, if there is a co-processor that is awake and responds to the network requests by accessing the hard drive, that would be one way to accomplish it.

If you're asking about a specific product or technology, that is off-topic here.  But conceptually, you can certainly build a computer that has this capability.  Whether any individual computer does have that capability is a question about that specific product or technology.