Website hosted someplace, WordPress blog another, same domain name?

Not sure how to word this but I’m being asked to develop a wordpress site that will not exist on the sam server that the main website is hosted on.

I assume ‘technically’ you could do htaccess on the main server and link any /blog/ site to the new server, but how would i keep the domain name?

Is my only option to do a subdomain? Does that screw my SEO?