Are they? This is a mystery to everyone except the barnacles themselves, which--may be up to a roll of the dice for young Sephiroth, if he wants to truly find out. Because Gorgug is hearing that question, glancing at the barnacles, and:

"I have no clue."

Are they moving? Are they magical, forever living despite horrendous conditions? Are they perhaps even being kept alive by the celestial energy that encompasses the van via the celestial being attuned to the van?

That's all to be decided...by Sephiroth('s next tag, those barnacles can be as dead or alive as you want).