Generally no, they don't. Unless that's something that Mormons used to do many decades ago. They usually just refer to non-Mormons as non-Mormons.
Gentiles only really come up when they're maybe referring to Jews as opposed to non-Jews in biblical stories/references.
Edit: Looking it up, does seem that what you're referring to was indeed an older habit from the 1800's and maybe early 1900's. Could possibly be different in pocket groups in other countries.
I think they call non-Mormons 'gentiles', which sounds very weird, but also does have a long history in Christianity as well.
Generally no, they don't. Unless that's something that Mormons used to do many decades ago. They usually just refer to non-Mormons as non-Mormons.
Gentiles only really come up when they're maybe referring to Jews as opposed to non-Jews in biblical stories/references.
Edit: Looking it up, does seem that what you're referring to was indeed an older habit from the 1800's and maybe early 1900's. Could possibly be different in pocket groups in other countries.
It's definitely something I've heard before. I think it was in an Orson Scott Card book, who is definitely very Mormon.