Hi Laurie,
I personally have had zero luck with Di Tan Tang (as theoretically appealing as it sounds). I agree, though, that a diet change is essential. I wouldn't stop at Z/D, though, and feel that complete avoidance of grains is essential. So a home-cooked or even raw diet is a good option. Wheat and simple carbohydrate sensitivities are most often associated with epilepsy, according to available research. So processed carbohydrate based foods are not helpful.
If the pulse truly is slippery, I would even just look at Si Miao San, despite the lack of Damp Heat signs. It's worked well as an anticonvulsant in these cases where diet may be a concern.
That being said, most Dachshunds are Yin or Blood deficient. So if the pulse felt feeble to you, rather than overtly easy to find but toneless, I would start with basic Tian Ma Gou Teng Yin, arguably most veterinarians' knee jerk choice for seizures, especially given its low risk of adverse effects.
Finally, what really clinches the diagnosis for me in these vague cases are the acupuncture points that fix or improve the pulse. Next time you see him, needle the points one at a time, and see which ones really make it a pulse 'you would want to own'. That way, if the dog is still not improving, I'll have a better idea what to do next.
Good luck with these ideas.
Steve