Can someone take insulin tablets ihey suspect they might have diabetes but are afraid to discover it?

Dangerous. Insulin or diabetes medications can severely drop your blood sugar causing confusion, coma, and possibly death. You do not want to use it unless you know you have diabetes. Diabetes is a life long disease so denying it will only prolong the inevitable. Eventually you will have to face it to be treated properly.
No. Insulin does not work as tablets, only injections. And it is important to see a doctor if you think you may have diabetes. As much as a diagnosis of diabetes can be scary the bad effects of poorly controlled diabetes are much scarier. Testing for diabetes is relatively simple and easy to do. It involves either getting a test done for a hemoglobin a-1 c or drinking a small amount of a sugary liquid and then having repeated blood sugar checks done.