The length of the arm determines capacity and to calculate capacity you add the difference between the largest and smallest cassette cogs to the difference between the largest and smallest chain rings. Since you have supplied only half of the needed information it is not possible to answer your question. Whether the derailleur can handle the 30t cassette cog the answer is "probably." It will depend on the specifics of your frame and of course the specific model of the derailleur, which you also did not mention. Search The official Campagnolo web site - Bicycle Parts and Components Cycling - Technical documentation for technical documents.
Strictly speaking, what you have is a "medium cage" RD.
Even though you have some unusual gearing - 33T ring and 30T sprocket, you should be fine with the RD you have. As always, it's important to get the chain length right.
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