Yes You can
It will not break MVC architecture,
You can check like this
if(!class_exists('VirtueMartModelUser')) require(JPATH_VM_ADMINISTRATOR.DS.'models'.DS.'user.php');
$usermodel = VmModel::getModel('user');
$currentVMuser = $usermodel->getUser();
First you should include the model file in the required model then create the object. then call like above. This example is Virtue-mart using method