I’m using Mercurial but I’m using the following as my branching model:

I have a feature that I’m working on, so it’s in it’s own feature branch. However, I have some smaller items I’ve changed in the development branch that I’d like to use while working on the specific feature way over yonder in the other branch. Is it permissible to merge development into that feature branch given this model? Or would that be violating this model?
No in common sense.
You made workflow violation earlier: when “have some smaller items I’ve changed in the development branch” – these changes must be in separate feature branch(es), which you can merge in your feature branch or (better) into temporary “combined” (your + side) branch: in case of ideal nvie-workflow develop-branch have to contain only mergesets from task-branches
PS – from other side “not man for the Sabbath, but the Sabbath was made for man” and you’ll have only dirty history in case of your merge