Ugh. I hate oil threads. As long as you use an oil without the friction modifiers then your bike will probably be just fine. If you do use a car oil WITH friction modifiers it won't ruin your engine but it will burn up your clutch. No, you don't need to run a full synthetic race oil on your bike. What's important is using decent oil designed for motorcycles and changing it at, or just before, Honda says so. My last toy bike was a KTM supermoto. I rode it semi-hard so I also changed the oil more frequently and I only put in the best full synthetic oil. I was paying roughly $22 a quart for oil on that. The Grom? I'll be running a full synthetic Mobil 1 or Castrol. Heck, I might even decide to use Rotella.
In any case though just remember that heat and friction break oil down. The Grom is air cooled which means in traffic it will get warmer than a water cooled bike. Because of this it's actually VERY important you change your oil at the recommended interval or, if like me you plan to do a lot of city riding in traffic, then you need to change your oil sooner than recommended.