The purpose of shadowing is to show med schools that you understand what you are getting into and that it is your life passion. You can list podiatrist shadowing, but it doesn't help show them that you are prepared for the long journey to become an MD/DO. It is VERY costly to train doctors, and schools absolutely HATE it when students drop out because it wasn't for them. Students with extensive shadowing that still show a high degree of interest are obviously more likely to stick with many years of extensive schooling vs someone who has only seen their PCP when he/she is sick. Definitely shadow other docs, pediatricians like you mentioned, etc.