It should not be a problem to simply point your DNS registration (.it) to a Lunarpages nameserver. I can't answer for sure your question about how a dedicated IP address works with this. I don't recall ever hearing that you had to change your DNS entry or anything like that -- is that what you're asking? I don't
think your registrar needs to know anything about your dedicated IP address. However, before committing time and money on my answer, I'd get a second opinion from support or sales. Just email your question to
support@lunarpages.com (which will open a support ticket), if
Mitch or
Katrina1 don't get here first with the answer.
If you bring your own domain name to the party, you will still be able to use a free domain name some time in the future. You don't lose it by not exercising that right immediately. If at some time in the future you want to get a domain (for an add-on) that the Tucows/Lunarpages registrar supports, you can get one for free.