Most gar will take to pellet foods ime easily when they are usually at the tail end of their first year.. there is a lot of bad information in this thread in reguards to Gar care and husbandry. I would suggest reading the stickies In the gar/bowfin subforum if you haven't already to help narrow down your choices/ideas.
Gar are Piscevores... meaning they eat fish.. its what they do.. the type and quality is what matters. another great option if you don't want to feed live but give your gar a solid diet ( ime pellets alone make my gar fat.. and fatty liver disease isn't healthy feeding.) Is frozen fish fillets from the market. I've fed a mix of live feeders/frozen fillets/pellets for many years and my gar have never contracted a disease. If you are concerned about this freezing most foods for 4weeks will kill a lot of stuff but not everything. and other foods such as worms have an extreamely low chance of carrying diease.
Make sure whatever you feed is a quality food, be it pellets or live. pellets imo are like vitamins and whole fish are better then fillets.. but fillets fed along with pellets are a great alternative.
Gar are not cichlids or the vast majority of "monster fish" they are specialized hunters. as for your poly mine always did best on a mix of pellets, and nightcrawlers.
lot of people are simply against live foods, and some of us pro. do your research either way you decide. and the sub-forum stickies for more in depth information is a great way to learn more if you haven't found them yet.