Theoden rode out from Edoras with a muster of "more than a thousand" (TT p. 528). They are described as "a great host of men, old and young," and were certainly almost all of Rohan. And yet, less than 10 of them were named--and among those named were an elf and a dwarf. Is it possible other friends of the Rohirrim of other races rode out that day? Tolkien doesn't say no.

Arriving at Helm's Dike, Theoden discovers that "Erkenbrand had left many men to hold Helm's Gate, and more had since escaped thither" (TT, p. 534). He receives an update from Gamling, leader of the outer defenses. Gamling tells the King that there are "maybe a thousand fit to fight" garrisoning the keep, "but most...have seen too many winters, as I have, or too few, as my son's son here." Furthermore, Gamling informs the king that the caves of the Deep also shelter "three parts of the folk of the Westfold, old and young, children and women" (TT, p. 535). This is a large number of additional people, albeit non-combatants...and, importantly, yet another place where a friend of the Rohirrim could arrive with them.

As Whart mentioned, there is one exchange between Gimli and Legolas which applies to this discussion. Legolas says, "But you comfort me, Gimli...I wish there were more of your kin among us. But even more would I give for a hundred good archers of Mirkwood. We shall need them" (TT p. 536) JRRT's wording was a bit vague, leaving us free to interpret it as we each wish. It could mean that Legolas and Gimli saw every one of the thousands of fighters and non-combatants throughout the keep and all its ramps and ramparts and passages and halls and tunnels, and are certain there are no other dwarves present (and no company of 100 Mirkwood elves). Or it could mean that there might be some small number of dwarves and elves around, but that Legolas and Gimli were not aware of them. Or it could mean that there are SOME of Gimli's kin there, but Legolas wishes there were MORE. I personally find it no great stretch to imagine a dwarf or two, and an elf or three among the crowded masses inside the hold. Not to mention some men who hail from lands other than Rohan.

Note that I do not intend to 'run circles' around the lore or 'assert loopholes' (not even sure what the latter means), as someone accused people of doing earlier. I am a huge Tolkien fan, and am as eager as any to see LotRO reflect LotR faithfully. I am simply pointing out, as others have, that "an absence of evidence" should not be confused with "evidence of absence." If you want to believe that you could be at the Battle of the Hornburg and still fit nicely within the lore of the Lord of the Rings, you certainly have the logical foundation to do so. I know I will. (unless you're a hobbit...sorry, lore really has a problem fitting you in)