Cranks and Bottom Brackets
 

I'm thinking about change my cranks on my Scattante road bike from TruVanta (not sure of the spelling) to Ultegra. Same length.

Question: will I have to (or should I) be looking to change the Bottom Bracket as well?

Yes , get the combination. new stuff attaches the spindle tube to the right crank arm,
and the external BB is part of the package design..

And as a plus , you can resell the other stuff as a package too..

Assuming both are external bearing type, the TruVativ may use the same size BB but I'd go ahead and get the Shimano BB as they are not very expensive and, as noted above, allows you to sell the old stuff as a set.