Brice,
Doing a keyword search for either will yield the record in question. If it's the only record matching that number, it will go directly to the results.
Often times, item number matches will also match a biblionumber, so you'll usually have multiple records in the search results for that. Barcodes are usually unique across all indexes, but if you have shorter barcodes, you may get multiple results with that search, as well.
It would be a small piece of development to add barcode or system number searching to the OPAC advanced search, since those indexes already exist in Zebra.
Cheers,