Is it possible to route a subdomain to specific template group?
For this example we have two domains:

http://www.example.com
http://subdomain.example.com


To use different templates for the subdomain, we can accomplished this with these steps:

1) Setup subdomain to point to a different directory on your server:

Domain: /home/wherever/public_html
Sub-domain: /home/wherever/public_html_subdomain


2) Copy your index.php file over to your new subdomain directory and update the CRAFT_TEMPLATES_PATH variable to point to the location you want to have your templates.  In this example, both template folders are above web root.

// index.php for domain
define('CRAFT_TEMPLATES_PATH', realpath(dirname(__FILE__) . "/../templates").'/');

// index.php for subdomain
define('CRAFT_TEMPLATES_PATH', realpath(dirname(__FILE__) . "/../templates_subdomain").'/');


Your template folders now look like:

/home/wherever/public_html
/home/wherever/public_html_subdomain
/home/wherever/templates
/home/wherever/templates_subdomain