I'll certainly agree that Tatius and the rest of the Lunar strategists have been building this whole siege up to ridiculous levels for deeply ritual reasons. I doubt that this has been shared with the rank-and-file.
Being marched out to the arse end of nowhere is one's fate as a soldier, no doubt about it. Being marched all the way out there just to then be intentionally sacrificed to up the magical quotient of the Red Goddess vs Orlanth slugging match is not what they think they're there for.
It's generally rather rare for the command staff to actually level with the troops. To take a real-world example, the most ground-breaking aspect of the Canadian victory at Vimy Ridge in 1917 is that every soldier, right down to the last private, was briefed extensively on what their particular unit was expected to do in the coming battle. Right down to giving them all maps! If the officer died, the non-coms knew what machine-gun nest to take out. If the sergeants and corporals died, same thing for the privates.
All units were actually rehearsed and marched over a mock-up of the battlefield beforehand, so that they could time their advance with the rolling artillery barrage. Oh, they all knew that the butcher's bill would be high. 100,000 French had already been killed or wounded trying to take the same hill. The whole area was an open grave. The eventual tally was 3,600 dead and 7,000 wounded out of 15,000 or so Canadians. Four received a Victoria Cross. However, the objective was clear, as were the plans, and it worked. http://www.warmuseum.ca/cwm/exhibitions/vimy/index_e.shtmlhttp://www.thecanadianencyclopedia.ca/en/article/vimy-ridge/
In this case, it's particularly unlikely that Tatius wants his army to know the truth about their long range purpose. Let the troops get the message that all they're really good for is to be lambs to the slaughter, and I think they'll vote with their feet (and everything else they've got). At the very least, their morale will plummet.
On to the current tactics of Tatius. Promising that the honoured dead are going to be protected from the zombie-raising ritual sounds good. However, all it takes is a little misinformation (and the natural scepticism of the average infantry type), and the troops may well think that these protection zones are in fact exactly where the dead will be made to rise.
An interesting point made in the second article on Vimy Ridge is that the assault happened on Easter Monday. So, the Canadian victory was tied to a religious date. It's elementary magic to make sure that you do your rituals on the best day. Push Tatius into postponing the zombefaction, and it's still a partial win for the Orlanthi.
Also, what about all the dead that were never properly buried? Sylphs must have been raising and dropping Lunars by the hundreds over the seasons the siege has been dragging on. Ernaldan earth elementals will have swallowed others up. It's not going to be a clean battlefield (as if any battlefield ever is).
Oh, and another thought added by Ian (just back from night school - sort of appropriate, that). So what stops these green curtains being messed about by sylphs, sneaky types, etc.? A stiff breeze or a sharp knife, and all that ritual protection is nullified. There can't be that many Shargashi.
As an aside, it was never part of the rules of 'Dragon Pass', but I would bet that when the generals decide to buy the Tusk Riders' help, the doomed legion has to be escorted by two others if the sacrifice is to come off. At least if the unit knows what the Tusk Riders' price is.