Generally, there are no problems with bringing a nanny on vacation provided you can afford it and both parties can come to an amenable arrangement. When you think about it, though, those are two fairly big ifs.
Remember, unless your nanny isn't expected to care for the kids on this trip, this isn't a vacation for him or her. It's therefore customary to supply the nanny with travel expenses, food and a separate room. Costs can add up quickly, so you might want to consider renting a house and buying groceries instead of, say, booking two adjoining rooms at a resort.
Consider, too, that your nanny might not want to go on vacation with you. A trip to Paris or Santorini is one thing, but spending two weeks snowbound in a secluded mountain cabin with no escape and nothing to do during time off might be somewhat less appealing for your nanny. Even a resort trip will pall if the nanny never sets foot outside because of an ill child, or if everything costs more than the nanny can afford to spend on a day off.
Finally, mull over what it will be like to be around each other in such a confined space. Are you the sort of person who considers vacations sacred family-only time? If so, having a nanny around might feel a bit intrusive. Expect some friction if you don't consider these issues before you ask your nanny to accompany you, or if you fail to lay out an agreement ahead of time detailing schedules, hours, expectations and duties.
That said, it's still manageable as long as you break it down, communicate well and follow a few helpful tips we'll discuss in the next section.