While it is possible Las Casas may have been present as some aspect of the Landa's trial, it is unlikely that the two had any meaningful interaction. For one, Las Casas was nearly 40 years older the Landa. By the time the latter man even arrived in the Americas, the former had already served his time as Bishop of Chiapas and, under pressure, returned to Spain. When Landa committed his infamous burnings in Mani, Las Casas' Short account of the destruction of the Indies was a decade old and he himself was only a few years from his death.

While Landa would have been familiar with the position Las Casas, his chief opposition in the Yucatan was actually the presiding bishop of the area, Toral, a fellow Franciscan. It was Bishop Toral who found Landa's methods extreme and his justifications for them lacking, and thus sent him back to Spain for judgement. While there, Landa wrote his famous Relacion de las Cosas de Yucatan, which mentions Las Casas not at all. He does, however, mention Bishop Toral several times and even notes in the passive-aggressive prose of 16th C. literature that:

At this point fray Francisco Toral, a Franciscan friar, and a native of Ubeda, who had been for twenty years in Mexico and then come as Bishop of Yucatan, arrived at Campeche. He, giving ear to the charges of the Spaniards and the complaints of the Indians, undid the friars’ work, and ordered the prisoners released.

The "friars' work" being undone in that passage refers to the work of Landa himself, in rooting out and punishing those Natives he considered apostates.

If there is an at least indirect rebuttal of Las Casas by Landa, it would be at the end of his Relacion where he says:

And thus they err who say that because the Indians have received aggravations, vexations and bad examples from the Spaniards, it had been better for them not to have been discovered; because those were still greater vexations and aggravations which they perpetually inflicted on each other, killing, enslaving, and sacrificing themselves to the demons. As to the bad example, if they have had such, or today have it from some, the King has remedied it, and daily does remedy it by his Justices, and by the constant preaching and persevering opposition of the men of religion to those who set such examples, or have set them; for the teaching is evangelical, and scandals and had examples are necessary things.

I put emphasis on that part because it is again a place where Landa is obliquely referring to himself and his actions. The Relacion may have been a historical document, but it was also a part of Landa's defense against accusation of abuse of his power and exceeding his station. We can see here that his argument was, in small part at least, that "constant preaching and persevering" was necessary lest the Natives slide back into their pagan ways. Those indigenous practice were, to Landa, worse than the temporal abuses of the Spanish or the harshness of his own methods, because their spiritual salvation through Christianity was for more vital. This is actually a far different argument than what Las Casas wrote about and is aimed at a far different audience.

Las Casas certainly wrote on spiritual matters, and indeed the whole of his debate with Sepulveda hinged upon matters of philosophy and theology. His primary audience though, was really about the secular legality of the Conquest and basic human morality of the actors involved. Las Casas was concerned with the destruction of peoples through the actions of conquistadors. Landa did, as did many of the clergy, concern himself with protecting the Natives from the abuse of secular authorities. His 1574 excommunication of the Governor of the Yucatan in fact sprung from accusations of cruel behavior towards the Natives. Landa's primary concern, however, was theological and even apocalyptic. He was concerned with the salvation of souls from imminent damnation. The impression of Landa that comes down through history is that he was there to convert some damn pagans, put the fear of God into those who backslid, and everything else was secondary.

So while Las Casas and Landa often get contrasted as a clerical hero and villain, respectively, their primary interests where really on different tracks of thought. Again, this may come back to the age difference. Las Casas, a friend of the Columbus family, was born in a world where the Americas were completely unknown and was among the earliest settler in the Caribbean. By the time Landa was born, Cortes et al. had already conquered Mexico. The two men were operating on different generational timescale of thought, and of location. The period between Landa being sent back to Spain in 1562 and Las Casas' death in 1566 was the only time when the two men were in the same hemisphere. So did they meet during this time? Maybe, but neither wrote about it and they weren't the arch-rivals as they are sometime portrayed.

PS - The burning of writings and idols about which Las Casas wrote had nothing to do with Landa, although they did occur in the Yucatan. The passage actually has to do with the Maya being angered that, although they acquiesed to the priests burning their idols, they were promised protection from the conquistadors, which the priests failed to do. Here's the relevant passage from his *Brief account...":

The Indians now findint the Promises of the Religious, that the Spaniards should not enter into this Countrey, null and void; nay that the Spaniards brought Idols from other places to be put off there; when as they had delivered up their own to the Priests to be burnt, that there might be only Worship of the true God established among them; they were highly incensed against these Friars, and addressed themselves to them in these Words following: Why have you deceived us, binding your promises with false protestations, that the Spaniards shoudl not be admitted to come hither? And why have you burnt our Gods, when others are brought from other Regions by the Spaniards? Are the Gods of other Provinces more sacred than ours? The Friers as well as they could (though they had little to return in answer) endevour'd by soft Language to appease them; and went to these Thirty Spaniards, declaring the evil actions they were guilty of, humbly supplicating them to withdraw themselves from that place.