I you want the other
website hostings also hosted here, all you have to do is to change the name servers to the name servers of eUKhost and to add the domain names as a parked or add-on domain on your account. That worked for me. It isn't necessary that your domains are registered by eUKhost to host the
website hosting here. By some registrars, you can enter the nameservers by yourself (two to three url's and/or ip's, two for eUKhost, see the email you get when you've created your account). By some registrars, you have to send an email to change the nameservers and some registrars even don't let you change the nameservers, in that case you have to transfer your domains to somewhere else (e.g. eUKhost) and you'll have to pay for a new registration. But it's rarely the case that a registrar don't let you change the nameservers.
Remark: you don't have to configure the DNS-records (CNAME, MX,...) by the other registrar, only the nameservers. The DNS-records have to be configured on the host where the name server is located (in this case, eUKhost and CPanel will take care of it).