I've got a few paid assets that just make things so much easier - I'm a programmer, so my art isn't the best ;) usually they're specifically stated as not being allowed, but nothing is said about it here! Obviously if I were to use them I'd make that very clear.

I'm not good at art

As long as they're properly paid for and credited as requested by the creator I say it's alright to use them.
It's more important that you started the game itself on or after the start of the jam.