I am strongly suspicious about the claim that one can directly perceive objects other than the ones we all perceive. I do not believe, e.g., in mystic perceptions. However, I am well aware that the argument runs circular unless it is soundly ground in ontology. To say that only what is perceived is perceivable does not add any information. On the other hand, anthropology proves that our perceptions are influenced by what we are used to think of as perceptible. Finally, I claimed elsewhere (see my italian blog on the Word as Instrument of Knowledge) that our sense perception can be altered by what we are linguistically aware of.
Whatever the case, the problem of whether dharma (and brahman) can be directly perceived is an intriguing one. Theists and followers of the Buddha, the Jina, etc., have to state that (at least some special ones) can perceive it, but they are then left with the risk of newcomers claiming they perceive it, too. "Traditional" Mīmāṃsakas are hard empiricists and stuck at the idea that "nothing beyond the physical world is perceivable", including in the physical world also inner sensations of pleasure and pain.