This brings my Rubenerd Database of Anime Pizza Hut References to four, as previously blogged. I'm sure there are far more.
My working theory is the Hidan no Aria writers decided to do this to further differentiate the series from Shana to deflect criticism that it's merely a stopgap derivative. I mean, pizza isn't melonpan!
That looks like a veggie pizza too, my favourite flavour ^_^.