My gut is leaning towards yes since those are variants on a PHB race, yes, but the variants themselves are only in that one book.
I always thought that Cambions (only considering Infernal Cambions here for simplicity) were half devils, whereas Tieflings were more distantly related to devils.
From the PHB, pg. 42:
Tieflings are derived from human bloodlines, and in the broadest possible sense, they still look human. However, their infernal heritage has left a clear imprint on their appearance.
… tieflings know that this is because a pact struck generations ago infused the essence of Asmodeus—overlord of the Nine Hells—into their bloodline.
And from the MM, pg. 36:
A cambion is the offspring of a fiend … and a humanoid (usually a human).
But then from Xanathar’s Guide to Everything, we have this table on page 62:
1-4 Both parents were humans, their infernal heritage dormant until you came along.
5-6 One parent was a tiefling and the other was a human.
7 One parent was a tiefling and the other was a devil.
8 One parent was a human and the other was a devil.
These last two entries on this table are what confuse me. So apparently a tiefling can be a half devil as well? Then what makes it different from a cambion? Is there a difference? Is a cambion basically just a “monster manual” tiefling as opposed to a playable race tiefling?
Note that I’m chiefly interested in 5e, but if information from older editions is required to explain this, I’ll accept that information too, but I’d prefer 5e information.
Mordenkainen’s Tome of Foes offers the option to select a different heritage for a Tiefling by replacing the default Ability Score Increase with its own (as well as by replacing the Infernal Legacy trait):
The traits of the chosen subrace replace the tiefling’s Ability Score Increase and Infernal Legacy traits given in the Player’s Handbook.
Swords Coast Adventurer’s Guide offers variant tieflings by either replacing Infernal Legacy (for Winged, Hellfire, or Devil’s Tongue) or by replacing one Ability Score Increase trait with another increasing feature (Feral):
Feral… This trait replaces the Ability Score Increase trait.
While a non-Asmodeus Tiefling subrace is not compatible with Winged, Hellfire, or Devil’s Tongue (since they both replace Infernal Legacy with their own option), a non-Asmodeus Tiefling subrace may be eligible for Feral (by replacing the subrace’s own Ability Score Increase with the Feral one). Is it?