I don't see why not if you also add other food items to the gar's diet in order to keep its diet varied and balanced. Pellets, algae wafers, market shrimp, and fish fillets are all good additions to the gar's diet.
whole silversides can definitely work as a staple...then just add the occasional pellets and you should be set. i feed whole anchovies as a staple and they have worked great for years (also in comparison to other staples). pellets are obviously formulated to provide a balanced diet and can be used as a staple with silversides as the accessory food too (i go with vice versa as some of my gars are pickier/less inclined to eat pellets for various reasons).--
--solomon
virtually no one is feeding live silversides (FW species are nearly impossible to keep alive, and unless you are doing some coastal fishing, the marine species aren't usually captured by the typical hobbyist); nearly all silversides in question are frozen fish that are purchased.--
--solomon