The lid of a Kettle and a WSM are formed differently.
A kettle lid fits over the bowl, and a WSM fits into the center section and will not fit its own base. A kettle lid will fit the base of a WSM.
I have yet to find an open 55 gallon drum that will accept a kettle lid without the soon to be patented swamprb Kettle Flange mod or flaring the lip of the kettle lid to fit.
Mine are removable to utilize the drum lid, rotisserie rings or the Weber lid.
The majority of closed drums that I have built have been able to accept the Weber lids without any mods. Just be sure to cut the top off inside the lip edge of the barrel.
The lids of a Smokey Joe will fit on 15 gallon drums.
And my 26.75" Weber Bar-B-Q-Kettle lid fits on my 85 gallon drum.
I also have an open 30 gallon drum that is too wide for the 18" Weber lids but the flange mod will take care of the fit issue. I'll probably make that a Winter project.
So to answer the original question - IMO, No - the WSM lid will not fit or be a suitable lid for a Drum Smoker. (but you can send it to me and I'll trade you a kettle for it!)