We were at Vero a few weekends ago with some family, and wanted to get a cake for my Mom's b-day. In-Room-Dining (or is it <i>Inn</i>-Room-Dining?!?) told me that, with 24 hours notice, they could do something very customized but, on short notice, it would just be your basic cake.
We went ahead and got it - and it was very tasty. Vanilla cake with that "cool-whip"-like icing (real light). They weren't able to write on the cake but, instead, put it on a silver footed-cake- plate and wrote "Happy Birthday Mom" on the plate, itself, just below the cake. They then sprinkled the cake and the plate with little Mickey sprinkles.
They said it would serve 6 - thought they were generous slices - and it was $12.
Also - if you have the time - there's a Publix nearby that could do anything you want. (I've grown up with Publix being here in Central Florida - and they've always been known for their bakeries...)
If you take a right out of the resort, take the bridge right there (CR 510) back over to US-1. Take a right, and there's a new Publix just up on your left - less than 10 minutes from the resort.