For the sounds used in main menu only: it’s GUI, that’s okay. Use your best judgement taking into account the spirit of the jam as well.
Regarding the multiple SFX point: Having different sounds assigned to button hover, activation, etc. could be an accessibility feature for low-vision players, as that's audio feedback for different actions. We fully understand that it may look a bit odd to have no restriction on the SFX for the UI but this is the reasoning behind it. Aside from the fact that we suspect most people will not really try to do much with it.