Is involved in the final hydroxylation step of the post-translational modification of translation elongation factor P (EF-P) on 'Lys-34'. Acts after beta-lysylation of 'Lys-34' by EpmA and EpmB. EpmC adds an oxygen atom to the C5 position of 'Lys-34' and does not modify the added beta-lysine (By similarity). Belongs to the EpmC family.