Yes, non-flammable liquids and gels, including frozen gel packs, are allowed in checked luggage by the US TSA. (Rules in other countries may be different.)
As with any liquid or gel in checked luggage, keep in mind that checked bags are regularly dropped, thrown, and crushed. So make sure that any liquid or gel is packed in such a way the it will not burst onto the contents of your bag (and other passengers' bags).
Also, all checked bags a x-rayed. Dense objects and liquids increase the chance that your bag will be opened for inspection.