Cant say I tried exactly what you describe, But SG does adhere well to rubber. I successfully glued shut a pinhole in a butyl tube and a cut in a clincher tyre. I say give it a go. Clean it up, glue the cut. If it doesnt hold, get the patch kit.
EDIT: Come to think of it, the sealant was supposed to close the cut in the first place and is touted to close cuts much larger than yours. In that light a patch should not be necessary. Glue should suffice.
Last edited by Racing Dan; 07-09-21 at 06:21 AM.