Is this considered spam?
 

If someone runs a site for Dodge Viper owners and goes over to another Viper site that has a forum with member emails...Is it considered spam to contact those people who's emails are listed and let them know about their site?

I would say no as long as they arnt sent like 10 emails a day for weeks

yes it is.
they never asked to be contacted. it's unsolicited.

Not spam IF the existing site does the mailing.