Can and in fact have!

The theocracy’s religious teachings buttressed its class order. The poor and afflicted were taught that they had brought their troubles upon themselves because of their wicked ways in previous lives. Hence they had to accept the misery of their present existence as a karmic atonement and in anticipation that their lot would improve in their next lifetime. The rich and powerful treated their good fortune as a reward for, and tangible evidence of, virtue in past and present lives.

The Tibetan serfs were something more than superstitious victims, blind to their own oppression. As we have seen, some ran away; others openly resisted, sometimes suffering dire consequences. In feudal Tibet, torture and mutilation--including eye gouging, the pulling out of tongues, hamstringing, and amputation--were favored punishments inflicted upon thieves, and runaway or resistant serfs. Journeying through Tibet in the 1960s, Stuart and Roma Gelder interviewed a former serf, Tsereh Wang Tuei, who had stolen two sheep belonging to a monastery. For this he had both his eyes gouged out and his hand mutilated beyond use. He explains that he no longer is a Buddhist: “When a holy lama told them to blind me I thought there was no good in religion.”[21] Since it was against Buddhist teachings to take human life, some offenders were severely lashed and then “left to God” in the freezing night to die. “The parallels between Tibet and medieval Europe are striking,” concludes Tom Grunfeld in his book on Tibet.[22]

The whole Parenti essay is fascinating https://redsails.org/friendly-feudalism/

Buddhism is not a theology?

This is a concept https://en.wikipedia.org/wiki/Nontheistic_religion

The part where you have enough social liberty that you don't have government officials telling you how to dress.

That would be good indeed, but isn't really an aspect of secularism.

'secular theocracy' is wordplay making fun of their attempts to secularize in such a way that they take on features of a theocracy, such as dress codes.

Fair point.

You could presumably have a Buddhist theocracy without any sort of belief in a supreme ruling deity.

I think that wouldn't make it a theocracy, as it's more of a philosophy or way of life rather than a belief in a higher being that has a strict set of rules that a state could enforce. But I don't really know that much about buddhism, so I might be wrong.