There has been endless debate on what orcs look like? Tolkien is considered to have been the creator of the most fantastic, mindless, evil minion in modern fantasy, but did he envision them as 'pig-snouted' goblin-men, or were they indeed once elves, twisted by Morgoth's evil magic into humanoid abominations?
As orcs entered the vernacular, writers, artists, and movie make-up specialists have offered a wide variety of orcs. Indeed, as D&D enthusiasts mix orcs with trolls, hobgoblins, and humans, they sometimes approach the demonic in appearance, but several 'genetic' variants prevail throughout our imagined collective of fantasy worlds.
The pig-faced orc may be an off-shoot of the interbreeding of orcs and devil-swine or were-boars, while the 'pure' orc remains what Tolkien intended: a grotesque mockery of elvish form and visage, barely (demi-)human, yet strong in physical attributes, maligned and mutated beyond recognition by the evil magicks of a thoroughly evil and dark power.
Peter Jackson's “Lord of the Rings” movie orcs reminded me of D&D mongrelmen; more deformity ridden mutants than goblinoid, while the “Morgul-rat” orcs were possibly the 'pure' strain of Morgoth's evil, twisted elves – and let us not forget Saruman's “Uruk Hai” orcs; nearly giants, driven, and indefatigable. These may well have been bred with Tolkien's trolls, or for the purposes of D&D games – ogres, if it were not for their possessed drive to follow orders, as well as possessing greater intelligence than their Morgul-rat cousins.
A D&D troll and orc combination would truly be horrible; cunning, resistant to order, having some ability to regenerate, and hating fire as well as the sunlight.
To incorporate the half-orc as player character, keep in mind that a pig-faced half-orc/half-human may be interpreted as a pig-snouted human; hardly passing as a member of the human race!
This lends credence to the theory that orcs, in their 'pure-strain' form resemble Tolkien's twisted and malformed elves, and allows the pseudo-fantasy-science of D&D mechanics to assume that half-orc offspring have a 10% chance of passing themselves off as human characters, albeit very ugly humans.