Catalyzes the cleavage of the N-Calpha bond of glycine in Nalpha-GlyT to produce 5-aminomethyl-2'-deoxyuridine (5-NmdU) on DNA as a step in the pathway leading to thymidine hypermodifications in the viral genome (PubMed:34522950). As a final result of the pathway of hypermodification, 5-acetylaminomethyl-2'-deoxyuridine (5-AcNmdU) substitutes for a subset of thymidines in the viral DNA (PubMed:34522950). These modifications probably prevent degradation of viral genome by the host restriction-modification antiviral defense system (PubMed:34522950). 5-N(alpha)-glycyl-dTMP in DNA + A + H2O = 5-aminomethyl-dUMP in DNA + AH2 + glyoxylate