I initially thought "yes", but then https://drafts.csswg.org/css-scoping/#shadow-names seemed to only apply to "global names" (i.e. names created by at-rules), which is not quite the case for scroll timeline names.

There's a discussion in #7916 in relation to anchor/CQ names, which seems to expect that names (also non-"global" names) are tree-scoped by default?

Either way, it would be good to state it explicitly.