Re: Automatic weapons?
18 USC §922(o):
(1) Except as provided in paragraph (2), it shall be unlawful for any person to transfer or possess a machinegun.
(2) This subsection does not apply with respect to—
(A) a transfer to or by, or possession by or under the authority of, the United States or any department or agency thereof or a State, or a department, agency, or political subdivision thereof; or
(B) any lawful transfer or lawful possession of a machinegun that was lawfully possessed before the date this subsection takes effect.
It would be legal for the security guards to possess automatic weapons under §922(o)(2)(B) provided that they were lawfully possessed by a private citizen before 19 May 1986, provided that they are employees of the owner or lessee of the data center and not contractors (Virginia Code §18.2-291). But since weapons in that category are a) extremely expensive and b) would not provide any additional utility for that job beyond, say, Mossberg 500s, it's about as likely as the guards being issued Bugatti Veyrons for vehicular patrol.