My students were writing essays in my RN2T cohort. When I have them write, I have no problem allowing them to use dictionaries – I will be going through and correcting their writing with them, anyway, and I think it can be valuable because it encourages them to be more creative with language, which in turn allows them to become more engaged in the learning process.
Allowing them dictionaries in this day and age means allowing them to pull out their cell phones – that's where the dictionary apps live, along with online (internet) dictionaries and such like. I don't have hang ups about this. It's part of the world as it is, today.
One student, Hojin, had his phone out and was grinning at it.
"Teacher!" he objected. He turned the screen away so I couldn't see it. Then, thinking… "How did you know?"
"No one smiles when they're using the dictionary, Hojin," I explained, sardonically.
"Oh. You're so clever!" He laughed. And he put his phone away.