I wouldn't do the slice method. In addition to what you stated in the question the other issue is that if it is the seed from a hybrid you most certainly aren't going to get the same tomato variety as from the parent. I live in US zone 8 so I am fortunate to have 2 growing seasons (second is a little shorter), so the delay in germination wouldn't be much of a problem. The delay may reduce the yield because some blossoms may not set fruit due to the timing and heat.
The problem with just putting the slice is that the gel encased around the seed inhibits germination probably to allow the seed to be eaten by animals and survive so that the seedling travels a little further. So for those with shorter seasons you are delaying germination a little longer if the gel remains.
So it is possible it would work, but you could also get a beautiful plant filled with blooms or green tomatoes then a cold snap hits you and you don't get to harvest any ripe ones (Greens under the bed to finish ripening with a banana or fried greenies).
It would probably be better if the tomato was squeezed in a clear plastic cup, the top of the cup was covered with a cloth or paper towel and secured with a rubber band and put away in a cool dry place. After the seeds had fermented and you get a gunk on the top then spray/wash with water to remove the gunk. The seeds that sink are viable and can be used, the ones that float aren't.
I have had volunteer plants in my compost without the fermentation, but as far as seed saving tomato plants I seem to have better seed germination/viability with my heirlooms (Box Car Willie, Mule Team, Azoychka) if I do the fermentation.
I can't comment on hybrids since I've been sticking with seeds from Heirlooms. I would guess that since their parents are mostly cherry tomatoes that they would sprout and may produce ripe cherry tomatoes before a cold snap.
So it depends on your growing season, days to maturity, yield and such. Again, I would prefer to increase the seed viability and get them in the ground. Just my two cents.