A promising development in the design of datacenters is the hybrid network architecture consisting of both optical and electrical elements. In this context, the joint problem of bandwidth allocation and VM-placement, a problem that only recently received attention in all-electrical datacenter networks, poses new and different challenges not addressed yet in hybrid datacenters. In particular, we foresee two issues: (i) the number of edge-switches that can be simultaneously reached using optical paths from an edge-switch is limited by the switch size, (ii) the dynamic creation of optical paths can potentially establish a constrained optical network topology leading to poor performance. We abstract the requests of tenants as virtual networks, and study the problem of embedding virtual networks on a hybrid datacenter, which translates to the joint problem of bandwidth allocation and placement such that the topology constraints of virtual networks are satisfied. We develop and analyse two algorithms for embedding dynamically arriving virtual network demands on a hybrid optical-electrical datacenter. Through simulations, we demonstrate the effectiveness of not only exploiting the already established optical paths, but also of using electrical network in embedding requests of virtual networks.