Catalyzes oxygen-dependent 5-hydroxyuridine (ho5U) modification at position 34 in tRNAs, the first step in 5-carboxymethoxyuridine (cmo5U) biosynthesis. May be part of an alternate pathway, which is able to bypass cmo5U biogenesis in a subset of tRNAs under aerobic conditions. AH2 + O2 + uridine(34) in tRNA = 5-hydroxyuridine(34) in tRNA + A + H2O Belongs to the TrhO family.