1- Ask for thier MSDS on the product. They are requried to have them and provide tham when asked. That should answer if it is fda aproved, what you want too look for is "GMP" Good Manufacturing Process
2- I have been told from multiple sources in the gas industry that most bulk Co2 comes from the patoleum industry and oillyness is the greatest concern. Ive never heard of Co2 being a source of DMS or cornyness in beer. GMP Co2 (or O2) should need no filters for food production use.
Brewmaster & Operations Director, The Fermentorium
"Your results may vary"