Can someone with essential thrombocytosis and high cholesterol. Take omega 3 fish oil and baby aspirin together?

Fish oil + aspirin. Use caution: both Aspirin and fish oils have antiplatelet (anti-clotting) effect and both together may have an additive effect increasing the risk of bleeding.
Likely. Omega-3 fatty acids do seem to have a very mild antiplatelet effect somewhat similar to aspirin, and as such may slightly increase bleeding risk. Most of the time this would not be concerning, and may even be helpful in a person with thrombocytosis. Regardless, i would certainly suggest you clear this and all other supplements with your pcp or hematologist first.
Should be ok. There are no interactions with fish oil and Aspirin that i know of if you are taking fish oil to treat your cholesterol make sure your doctor is aware and that you are not doing it solely to avoid doctor recommended medication.
I assume you're. asking for someone older than yourself. Bleeding from fish oil is theoretical but in clinical practice is not a problem and the cardiac and other benefts are real benefits. Aspirin though does cause bleeding by platelet inhibition, use caution. The best test for bleeding is your symptoms.