Orchids produce very large numbers of very small seeds. Is each seed the
result of an individual pollination/fertilization event?

Theoretically, yes. While there are orchids which are apomictic (reproduce
wuthout being pollinated) and even cleistogamous (self fertilize in a closed
bud), the above is normally true.

Does the one pollen grain, one ovule, one seed rule apply?

Yes, as far as I know.

With the simplicity of orchid seeds, is it possible that more seeds are
produced than pollen grains involved?

Anything is possible, but as far as I know, it is not a normal occurrence.

It would seem that the number of pollen tubes necessary to result in the
massive number of seeds produced would destroy the integrity of the stigma,
style, and ovary.

There isn't any style in an orchid flower. The ovary & other necessary parts
grow to accommodate the pollen tubes.

Also, when orchids are pollinated, can more than one pollinium be involved?


Possibly, but I assume the excess pollen would be lost.

How many pollen grains can be contained in an orchid pollinium?

Don't know, but it is a pretty large number.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)