Galvanized Gutters Required For Dormer With Rubber Roof?
This study demonstrated not only no increased corrosion near an EDPM o-ring on an aluminum sample after 4 years immersion in salt water, but actually a lack of corrosion where the o-ring protected the aluminum from contact with salt water. The unprotected surface of the aluminum did corrode, but that's normal (it's salt water, not rainwater...)

EDPM is the normal material of rubber roofs. Rubber roofs are often secured with aluminum edge trim. 

Find another gutter guy; this one's a scam artiste.