Sow seeds under mulch?

These year I have been experimenting growing vegetables and grains different ways to see what suits me the best. I tried to grow spelt and black oats under mulch and both sprouted through the mulch and made a good harvest despite no watering, weeding or fertilizer. I also tried to grow vegetables using the same method, but the transplants(mostly tomatoes) and other flowers(borage, phacelia) outgrew and shaded out the vegetables(mostly carrots, beets, salad,radish). The seeds were a few years old so maybe that affected the germination, but a few carrots, beets, salad and a lot of radishes came up, but not enough to see if the experiment was a success or not.

I have seen videos of Holzer and others when they throw seed mixes and then mulch and that work for me with grains, but do vegetables have a harder time trying do push through the mulch than grains or flowers like phacelia and borage? Is the mulch just a winter cover for the seeds and soil? Do any of you sow and mulch like Holzer does?

I believe that some of the vegetables germinate best if only sprinkled with a bit of dirt. This could mean that light is a factor in there germination.
The Holzer way is putting out seed by the bucket so a low rate is not a problem and I guess he does it intentionally to load the soil with seed that will spring up every place as soon as there germination conditions are met - kind a like weeds but edible.