Yes, orcs are continuously depicted as cannibals (or, if you prefer, anthropophagous) in D&D lore.
AD&D 1e
Monster Manual, p.76:
They take slaves for work, food, and entertainment (torture etc.)...
Basic D&D
Orcs of Thar: I couldn't find anything on cannibalism with a quick scan, but this is an inordinately goofy book anyway.
AD&D 2e
Monstrous Manual:
Orcs are carnivores, but prefer game meats or livestock to demihumans and humanoids.
This is repeated without comment in PHBR10 The Complete Book of Humanoids. Sounds like they will eat people, but as a secondary recourse once the burgers and brats run out.
D&D 3/3.5e
No comments one way or another in the core books or Savage Species. There are parenthetical references to orcish cannibalism in non-canon sources, like this WotC blog article.
Pathfinder
Orcs of Golarion, p. 5:
Cannibalism
Orcs are infamous for their willingness (even eagerness)
to eat other humanoids, and sometimes even other orcs.
At some level, the practice is a matter of survival—eating
what food is available to them. In lean times, humanoid
slaves are more important to an orc tribe as livestock than
they are for their labor. After all, orcs can always raid for
more slaves when the opportunity presents itself later.
Orcs also believe consuming the flesh of other creatures
allows the eater to take on their strengths. Just as warriors
feast on the hearts of dire boars, cave bears, or worgs, so too
does eating a fallen enemy symbolize the ultimate victory:
not merely defeating the foe in combat, but consuming
all that he was.
As with other orc meals, humanoid flesh may be eaten
raw, torn from the body of a fallen enemy or a helpless
prisoner, or slowly and carefully cooked. Indeed, orc
“cooks” are just as often also butchers and torturers,
skilled in gutting and bleeding victims in such a way as to
“tenderize” them for slow roasting or stewing. Orcs often
talk about other races in terms usually reserved for livestock
and game animals, comparing the flavor and texture of elf
to dwarf, or the taste of this nation of humans versus that
one. When a laughing orc refers to a prisoner as “meat,” he
is being entirely literal.
D&D 4e
Monster Manual p. 205:
DC 15: Orcs favor hills and mountains, places pocked
by caverns easily turned into defensible lairs. Bloodthirsty
marauders and cannibals, orcs venerate Gruumsh and
thereby delight in slaughter and destruction.
D&D 5e
However, neither entry on orcs for 5e (Monster Manual p. 244; Volo's Guide to Everything p. 82) makes them out to be cannibals, merely murderous.
The races are mostly fine
I would replace Tsunami with Control Water for the Neptunian. An AoE spell that does half damage on a successful save is mediocre for a Druid, but better than great for a Fighter1.
The same is true for Lightning Arrow for Jovian, make it once per long rest.
Olympian
As David Coffron wrote, death saving throws should not matter much between magical healing and good encounter design, and Thaumaturgy is mostly for flavor, does not add much to power.
Base race is fine.
Minervian
While two +2 are very rare, only the Mountan Dwarf has it, this combination is much weaker, basically the second worst after +2 Wis / +2 Cha.
I would much rather pick +2 Wis / +1 Con (or Dex)2, so you are way behind a Half-elf.
This also makes the two skills fine.
Legend Lore has expensive components, and is not combat related. It does not add much to your power, while flavorful.
Hermian
Again, way behind a Half-elf for anything that needs Cha, but I could make a decent Cleric or Wizard with it. Still, a Variant Human is better.
Overall interesting and versatile, but far from strong.
Jovian
Looks really similar to the Fire Genasi, you should tie the spells to an ability.
We have a much earlier fly speed precedent with Aaracokra, and Control Weather is mostly for flawor, so this is fine too.
Neptunian
Very similar to Jovian, while Shape Water is significantly weaker than Shocking Grasp. Tidal Wave is comparable in damage to a 16th level Dragonborn's breath, but they get to do it once per short rest. I think it is ok, considering how mediocre the rest is.
As mentioned at the beginning, replace Tsunami with Control Water.
1) the expected damage of an 8th level area spell is 45,5 according to the DMG, but Tsunami only does 33 in the first round, even worse on subsequent rounds. A Druid can do better damage against mobs of weak enemies, and use his concentraion more effectively, but these weaknesses do not apply to a Fighter
2) You mostly need only 3 abilities: Attack, AC and Con. Some classes can merge the first two, but no-one needs both a high Int and Wis.
Best Answer
Orc sub-races are not yet in 5e
As you noted, Volo's Guide to Monsters doesn't do this but a future supplement might. Given how orcs have become more humanized in recent editions, in terms of their background and culture getting a little more meat on them than "big humanoids with axes and fangs," it would make as much sense to make sub-races of orcs as it does to make sub-races of humans - which 5e doesn't do either.
The game doesn't need them, but any of us as a DM or world builder can expand on their basic features in our own campaigns. I played in a friend's game a couple of years ago where the orcs were a high plains culture who often rode on aurochs - great fun. Borrow what you like from previous editions and fold them into your D&D 5e campaign. DMG pages 285-288 provide some guidance there, as do pages 273-282.