Sure, but what do they do? Looking at Google Brain for example, "research scientists" are exclusively people with doctorates, while "engineers" only require an MS or BS/BA.
The work is totally different; they're not substitutes.
I am not sure about Google, but when I was at Facebook, any Software Engineer with PhD can opt to use title Research Scientist instead. The purpose is mostly to make Green Card application easier.
When some people FB Core Data Science came to campus, they made it pretty clear that they were looking for people with doctoral training for their research work (and not, for example, a Master's graduate who completed PhD-level coursework), so I guess it depends on the task/team.