So yes, as long as you use your own Volume Licence key and media, you are covered by the OEM licence for each machine.
Re-imaging rights are a benefit granted to Microsoft Volume Licensing customers.
Microsoft Volume Licensing customers may use Volume Licensing media to re-image software (including OEM Software licenses) under the following conditions:
The copies re-imaged from the Volume Licensing media are identical to the originally licensed product (the same product and version,
contain the same components, and are in the same language).
The customer must purchase at least one unit of the product required to be re-imaged through their Volume Licensing agreement in
order to obtain access to the product media and receive a key.
Volume Licensing media must be used for re-imaging (OEM media may not be used).