Yeah, even if you get a character after the event is over, you'll be able to see their summer skin. This, however, doesn't apply to the additional poses that you can pull from the gacha.
So if you get a 3* Ashigara, you can see his summer outfit but you need his time-limited summer gacha 5* if you want to see him licking that... cone.
On another note, the quests will run till 18th September so getting everything, even without many superstar units, should be doable.>>3113
Managarmr seeema a bit too scrawny to me. The way his waist indents looks a bit weird.