Protein inhibitory process
No, absence of an stimulating substance is not appropriate to consider as inhibition.

To see why, consider a situation where there are two such substances, substance A and substance B, which can both stimulate protein P (many such relations exist).  If you add only substance B, then protein P will be stimulated. Since P is being stimulated in this case, it would thus not be reasonable to describe the protein being inhibited by the lack of substance A.