If you place a specific folder into the Global exclusions, then yes - they won’t be scanned at all. If you placed them e.g. only to the list of FileSystem Shield exclusions, then it wouldn’t apply for on-demand scans.
But honestly, the whole scenario isn’t really good… it’s not the same to scan files manually, compared to real shield detections. The shields have additional context (e.g. where the file is being downloaded from) they can use when deciding whether a file is good or not; on-demand scans don’t have that information - so some things may go undetected.