1. I think that kind of puzzle is just what you called it -- a Definitions puzzle. The description of a Definitions puzzle from the Theme Types
page seems to match your description.
2. It probably all depends on how fresh and lively your theme entries are and how good the rest of the grid is. I don't think any theme idea is necessarily an automatic rejection, but there are a handful of themes that are likely not worth considering because they're either too simple (i.e. themes that use colors like red, yellow, blue, and green) or the publisher has made clear that they're trying to avoid using them (i.e. I once received a NYT rejection e-mail from Paula Gamache that said that Will Shortz doesn't run many puzzles using quotations as a theme).
For what it's worth, the NYT recently published a puzzle
of a similar type that you're hoping to do, using the word "Bolt" in the clues as the theme unifier.