Yep! In fact, the U.S. Supreme Court decided a landmark copyright case that involved them, although tangentially. In Feist, the Court held that entries in a phone book were not, by themselves, copyrightable. The Court acknowledged that "[f]our of [the listings] were fictitious listings that Rural had inserted into its directory to detect copying," but didn't discuss the importance of those beyond that statement.

https://en.wikipedia.org/wiki/Feist_Publications,_Inc.,_v._R....

https://en.wikisource.org/wiki/Feist_Publications_v._Rural_T...

https://en.wikipedia.org/wiki/Fictitious_entry