You'd use "individuals" in the second use of creature in this context, but short answer is yes, keeping in mind the definition of species is largely arbitrary.

There's much more that goes into the definition than reproductive ability, so for example a lot of birds that are in theory different species are fully capable of breeding with a different bird species.

Then of course there's the coywolves and coydogs. Fully fertile (as far as I know), arguably better adapted to the niche than either coyotes or wolves, they'll probably be recognized as their own species at some point.