You will find that it is FAR more work to integrate Magento with OpenERP that it is to simply migrate your ecommerce to Odoo's ecommerce module. The maintenance of a home-built integration is substantial; you should consider this to be a full-time role.  

If you need to integrate OpenERP with Magento, I would host OpenERP in a different server. You might integrate it with Magento using the connector module, or you might develop your own scripts to do that. There are many cases of integration with other e-commerce packages where that integration is carried out by python scripts

Magento connector are not part of the official base, so it is not available on the saas.