Repoman doesn't complain about USE flags in DEPEND/RDEPEND (or "use foo && dofo" statements) when they aren't in IUSE. IUSE="" shouldn't be valid in cases like that.
Detecting IUSE in {,R,P}DEPEND and SRC_URI is easy enough... They are required to end in a ?. As for the inline use in an ebuild... That's a little harder.
Repoman complains about this now, as should the use func.