I can't see a problem with that dress, but do check the rules and if you can some previous photos.
For both my DD they have worn summer dresses, neither had anything to hook the cape onto it just say on their neck or got pulled down. This is for Science based degrees at Russell Group Unis, so not arts or anywhere more known for being different.
DD1 wore a cream dress with flowers on, with the main flower being in the same colour as the strip on her gown. The dress has thin straps and is just below the knee. She wore high heeled open toe sandals.
DD2 has graduated twice, both times in a posh dress, for her summer graduation it was bright pink, below the knee with long sleeves, she wore open high black sandals. The pink under the gown looks really good and red will too.
For the winter graduation (it was trying to snow), she wore a mid thigh cream dress, fake tan and chunky boots. The other girls on her course wore summer dresses and either boots or sandals. The boys are all in shirt, tie, suit trousers and formal shoes