Yup, you can definitely hear the engine just fine with earplugs in. Even the best ones don't mute the world, they just turn the volume down to safe levels.
I do find that when I'm riding to the gas station without plugs, I can now hear some of the higher-pitched rattling or other unpleasant engine noises that are more muted with plugs. Put the plugs back in, and the engine sounds fine.