For general diving yoke attachments work fine but there are reasons you want to use DIN on a slung pony.
In general, slung ponies are dived with the valve off (though the reg should be charged before the dive). This poses two problems for yoke regulators:
1) It is easy to mix up the valve handwheel and the yoke attachment handwheel in an emergency because they look and feel similar. If this occurs, the diver will loosen or remove the regulator from the valve rather than opening the valve, with potentially serious consequences. While charging the regulator before the dive does help with this, there is no guarantee the system will remain pressurized. DIN valves don't have this problem because the attachment wheel is located between the valve and the reg making it look and feel very different.
2) Yoke valves are prone to ejecting the O-ring if the regulator is not fully seated on the valve due to misalignment, bent parts, or insufficient tightening of the handwheel. This can happen even to experienced divers. There is no reliable, effective way to correct this once it occurs underwater. DIN valves don't have this problem because the o-ring is captured inside the connection.