Let me put it this way. I am asking for a change in clerical Alignments, I am not saying you cannot be an Lawful Neutral Monk of Yurtrus, I am not saying you cannot be a Chaotic Neutral Wizard of Velsharoon. Heck, I've seen True neutral Rogues of Mask.
You worship an evil deity, the deity is Neutral evil, so he does what he wants without concern of how it effects others at the same time he benefits as well. They are normally cold, calculating evil deities who know the value of prudence and patience but at the same time are not afraid to do chaotic, or lawful acts when it best suits them.
A deity like Yurtrus, for example, is a god of plague and death. While non of these are inherently evil, the deity makes them in an evil light.
Orcs are predominantly evil race, chaotic, bickering beings. A LAWFUL orc of a stretch, but could be possible if he construed death and plague to be systematic, striking within a pattern. At the same time it could be CHAOTIC, striking whenever it pleases without rhyme or reason.
Combine the two and you got Neutral, this is when the cleric sees a system of plagues, whenever a population becomes to great a plague comes forth and begins to wipe them population out letting those who are strong enough to survive to reproduce and therefore become hardier to further plagues. The chaos aspect here is sometimes a plague strikes a smaller population, why? Because a carrier entered a relatively small tribe and they were wiped out.
It didn't develop naturally in the small tribe, it appeared in a larger.
Dogma: Death is inexorable and eventually claims all life. The ravages of plague are simply death claiming victims who have yet to fall in battle, leaving all creatures to simply choose the manner in which death will most likely strike. The touch of White Hands can be forestalled only by bowing down to the Rotting Lord and begging his mercy, but, in time, plague strikes all living things. Fear him, for death lurks in the shadowed corners of Luthic's cavern and it will inexorably come again.
The dogma of Yurtrus is un-equivocally evil. He uses plague and death to strike fear into the hearts of the Orcan population. The only Neutral aspect or Lawful neutral, or Chaotic neutral, aspect is to say that these are NECESSARY functions of life. That plague is required to eradicate the weak of stock. However, that would be a druidic outlook, and Yurtrus doesn't possess Druids. A cleric would use this dogma to make the Orc tribe fear HIM and bow down before HIM. And giving plague to those tribes or members who do NOT. At the same time, Yurtrus is asking you to kill every last elf, dwarf, and goblin, or basically anyone who isn't an Orc, that sort of screams evil to me.
The dogma can be construed to be Chaotic evil, or lawful evil, in ways I truly can believe Yurtrus would like.
Shar is undeniably evil, she is what I would call an 'elemental' force of evil.
Mask is evil, for what he does is wrought of greed and selfishness, taking the hard earned labors of others for himself.
Now when we examine Velsharoon, we see an eternal pursuit of knowledge, where knowledge is power, and the obstacles to said knowledge is to be destroyed. The singular most powerful obstacle is death, and to over come this, Velsharoon preaches an entrance to the realm of undeath to garner eternal knowledge, to live forever, forever learning. UNDEATH IS A PRIMAL STATE, THE VERY ACT OF SUMMONING UNDEAD IS EVIL, AND THE VERY ACT OF BEING UNDEAD IS EVIL. The only reason why a Velsharoonite would be LN or CN is because he finds undead distasteful, news flash, Velsharoon may be a god, but he's an undead god, the patron of all evil lich's. The worship of Velsharoon is the attempt for immortality, ways to stave off death, which leads most to the realm of the undead, and to become undead themselves.
Neutral undead are the exception. Evil undead are predominant.
Neutral orcs would be the exception, not the rule.
Orcs are what we would call, "Naturally evil." Born evil, given time alone, they'll raid caravans, rape women, and figure out the strength makes Right rule.
A half orc cleric would likely have grown up amongst the tribe of orcs to even been a cleric. Since tribes by large majority are evil, then evil clerics of NE gods should be.
So I don't even know why the Orcan gods even offer Neutral places for clerics. Orc=evil.