Hello UC,
This is a relatively straightforward type of 1:n integration from a Dynamics ERP and Dynamics CRM. I am including a blog posting at the end of this reply that also has additional information on how this can work.
Since you are only moving data into CRM from ERP, and not creating orders or contacts back in from CRM, then creating maps between each of the ERP's and a single CRM organization is entirely possible and supported. If you think you may have a future need to push data back into the ERP, then I would recommend a thorough plan around how ERP companies map into your single CRM organization (such as by using Business Units) in order to support bi-directional (if that may ever be in your plans).
Thanks,
Jeff