Actualy, he can use his real name and fool Wakana too
Has she mentioned not knowing his name before? She might have seen his name in paperwork before, and she doesn't have a mental block preventing her from noticing. Regardless, he'd only enter the contest to satisfy Wakana's dare; he wouldn't want to actually win.
For more speculation, Uta was bizarrely good in that rap battle and makes for an interesting dark horse. It could add some emotional setup for her next slate of events.
Also, rewatching the event where Wakana goes over the first submissions, she mentions a rule that a submitted poem can't be taken back or edited. Almost certainly an extraneous detail, but I'm taking it as setup for my "Akira unwittingly submits something crazy and regrets it" idea.