Modifier 25 definition is a significant, separately identifiable evaluation and management service by the same physician or other qualified health care professional on the same day of the procedure or other service. I don't recall seeing a definition of "other service." I would not consider medical supplies a service, therefore would not add -25 to the E/M if the only codes billed were E/M and a supply HCPCS. To me, procedure or other service would include things like an xray, ultrasound, biopsy, etc.
That being said, if the carrier were to have a policy to only pay the E/M if it had a -25 along with the supply, I would follow their policy. I'm not aware of any carrier with that policy, but you never know what crazy guidelines they will make up.