I think in the old days (until 20 or 30 years ago) most were real. Some used available engines like Continental and CAT but only a few were rebranded (like Ford and Ferguson). the lawn mower business is even more chaotic. My understanding is that MTD also directly makes Cub Cadet, Yardman, Huskee, Troy Bilt and others. They make lawn tractors for Deere, Husqvarna, Toro and many others but to the purchaser's spec, so they are not exactly the same as an MTD. We all know there are a limited number of engines, transaxles, spindles, etc used in small tractors, so many of the parts are interchangeable even if they weren't built by the same company.
Toro is interesting. My understanding is they are still an independent company and make their own snowblowers, etc. but they contract out the lawn tractors because they really have no history in that area.