Can you share the inputs you used to land Down Throw > Dash Attack on Fox at around 41%? I could not get the Dash Attack to work on 0° DI because Fox reached the ground too soon.
I tried it at 70% and it does work at this %. However, while the tech trap works, it does not give you enough time to Dash Wavedash to Fox's landing spot unless he DIs towards you. I tested for 135° DI but anywhere around that should give you a chance to techchase. If he does not DI, or DIs away, you will not be able to dash wavedash to his landing spot, which will make techchasing on reaction much more difficult.
Once you get to about 70%, it is better to follow the 0° DI from Down Throw with something like Down Smash. I don't this tech trap will be useful at all against Falco or Captain Falcon, considering how hard it is to land Down Throw > Dash Attack on someone as light as Fox.
With regards to techchasing off Dash Attack in general, the same things that I wrote for Down Throw techchasing in the OP apply to Dash Attack as well, assuming you can get to the landing spot and be actionable by the time you need to react. A very simple summary of that is:
1. Dash Wavedash to the landing spot
2. Up tilt, Forward Tilt, Down Tilt, Double Jab or Down Smash to punish tech in place.
3. Dash Grab, Dash Attack or Down Smash to cover techrolls.
4. Jab Reset the missed tech, or treat it like a tech in place against players who SDI the reset.
In the case of Dash Attack to start a techchase, getting as close as possible to your target before hitting them helps quite a bit. If we use Fox at 45% as an example, the Dash Attack will carry Yoshi to Fox's landing spot on its own, so you don't need to worry about getting there. If Fox DIs away, you will have more limited options but you can still cover his tech in place with Forward Tilt, Down Tilt or Down Smash without having to move after your Dash Attack. You do also have time to walk forward too, which helps you get a little closer. This isn't necessary but is very easy since it can be buffered.
I tested again at 75% with no DI, and it is harder to techchase. You have to land the Dash Attack very
close to Fox if you want to cover tech in place without walking forward. In most cases you will need to walk forward, and I don't think there is any way to cover tech in place or techroll away on reaction if Fox DIs away. If he DIs in, it will be easy to cover, just like it was at 45%.
At higher % (again, tested at 75), weak Dash Attack does become viable for techchasing if you can get a very late hit. Instead of the Dash Attack bringing you to the landing spot, you will have to Dash Wavedash. I tested on no DI, and it works but just barely, so it should work well against DI in, but not against DI away.
Against other characters, you will have more time to move after the Dash Attack, but obviously the floaty characters won't have to tech if they DI in.
Unfortunately Dash Attack has enough endlag to make this difficult to use as a techchasing tool unless you get a hit that will carry you to the tech spot. There usually isn't enough time to make any extra movement like you would do after other moves like Down Throw, Nair, Ftilt etc. However, if you do get the close hit, it is pretty easy and rewarding to techchase off Dash Attack.