There is seemingly some confusion about this issue of adjustment under INA section 245(a) as our USCIS denial letters quote the alien's ineligibly under 245(i). There is no question that after three years the U-Visa holder can adjust under 245(m), but then they must wait another 5 years before becoming eligible for naturalization.
However, there are valid legal arguments to support a 245(a) adjustment for an immediate relative, as the 245(c) & 245(k) bars are waived for immediate relatives.
I think the issue is not something that the Vermont Service Center has exclusive jurisdiction to decide, as it is their sole determination that no U-Visa holder can adjust under 245(a). As some U visa grantees first entered EWI, however the regulations state that they were lawfully admitted to the United States on the date the U visa is granted. This is aside from other inadmissibility issues that may arise.
I focus this response on an EWI granted U visa status that has not left the United States after the initial EWI. I'm in the 9th Circuit and we have Garcia-Quintero v. Gonzales, 455 F.3d 1006 (9th Cir. 2006), where the 9th Circuit held that the family unity grant rendered Garcia-Quintero admitted for calculation of the seven years for cancellation of removal for legal permanent residents. "Our decision focused on the aliens’ acceptance into the Family Unity Program”. Id. at 1015. As part of that acceptance, we looked at Garcia-Quintero’s enrollment in the program, specifically noting that it provided protection from deportation and that FUP beneficiaries “shall be inspected and admitted in the same immigration status as the alien had at the time of departure.” Id. at 1017-18. A U visa grantee received employment authorization, is protected from deportation and the language of the regulation states that they are lawfully admitted. Same benefits as that received by a family unity beneficiary. We deal with legal fictions all the time.