My 3 month old snores. Loudly. Is he ok? More risk for sids?

OK, no, but sids? no. Snoring could be a sign that large tonsils and adenoids are too big. Obstructive sleep apnea affects sleep, attention, energy and development, and over time can lead to heart damage. A sleep study should be performed to see if he is getting good oxygen into his lungs or if there are apnea issues. However, sids is an infant phenomenon for other reasons, not snoring.
Snoreing?? I've known many 3mo to rattle a lot with breathing but never heard of one snoreing. Your physician could verify an adequate airway for your baby & give you guidence on ways to improve the noise. We don't understand enough about sids to say yes or no. Keeping babies sleep area free of odors/perfumes/incense/smoke etc. & washing out the nasal passages with saline is what I do for congestion.
Upper airway lok see. Sids is not a problem, but he may have an upper airway anomaly. Discuss with your pediatrician. He may want to get an x-ray of your child's upper airway or perhaps send you to anent specialist for an evaluation.