First off, No never been asked that. But as a response, First thought is...Why?. Kinda ruins the portability of the leads. Then, what type of conduit are we talking about? Then, If that is what you want...your the customer. Conduit, Wire Size & Wire Type would all be factors to do the installation correctly.
When I was wearing the tools, I was asked to run the "hot" lead to several places in the building that was aboyt 20k square feet and then the welder was left in one spot (in the shop) and the person doing the welding only had about a 25' stinger lead that would be plugged in to various outlets via a cam lock type connector. The Ground was usually established via the piping or conveyers throughout the building.
The other installation where I was involved as the Inspector not an installer, had to do with a coupla sports events ( the US PGA Open and the Rider Cup) where the welder cable was used for feeders and branch circuits. This was however not in a raceway and this seems to be standard fare for this type of event. I'm not sure this is kosher but it sure worked well and was practical.
Any information on the use of welder cable for other than secondary conductors for a welder would be appreciated.