Although the main ingredient in sambal oelek and gochujang is chili peppers, they are not interchangeable in all recipes. Gochujang is thicker and has a sticky paste texture whilst sambal oelek is waterier and like a sauce in terms of consistency. However, if you use 1-2 tablespoons instead of 3 in both the meatballs and glaze mixtures, you can certainly substitute it and make sambal oelek meatballs instead. Also omit the vinegar from the glaze as sambal oelek already has it incorporated in it and will be tangy enough.