The Guard recruiter is giving you accurate information, people in reserve components are not on any orders when not drilling, training, working, etc. USUHS and the Navy's HSCP are the only options for being on orders throughout medical school and both incur years of active duty obligation after medical school. Your second question is irrelevant because drill status is not going to get you USERRA protection.
Even if you find a potential avenue to make this work, I would speak with a lawyer if this is important to you particularly since it's going outside of the intended purpose of USERRA.