Well, once again, to respond to my own question, it seems that LaTeX's
\begin{quotation} \end{quotation}
is considered an "environment," and not really a "paragraph style." So treating it as such in Ulysses exports what would be semantically expected.
The LaTeX quotation environment might be better handled as a "markup style," I guess, but I'm not sure that's what the Soul Men intended markup to mean.
(A further observation: once you get into editing the LaTeX template, it's unclear to me whether you can create anything other than inline or paragraph markup. I won't have time to experiment with this until later...)