Thats strange, I thought the norther you go, the more people care to speak proper high german. Irgendwer (and irgendjemand) have a stronger conotation of uncertainty. Jemand is an unspecific person, irgendwer is a "really" unspecific person.
I see the problem now. I was thinking of "someone will go with you" as "they will go with you" in English since "they" can be singular or plural. But "they" would refer to a specific person if singular. Danke!