Claudia, if you are still looking here's a tuppence...

In the last few years I have gone from programming in C++ to VC++ / COM to Java to C#. It is true that all of the languages have similar constructs and are easy to learn if you know one. However there is a BIG shift in mindset going from doing C++ to Strong GUI Based applications.

If this person is going to be part of team or be paired with others who have had previous exposure to Such Event driven UI programming (as Java/VC?VB or Web apps) then go ahead without doubt. However if this is going to be the only person/tech lead in developing this application. I would give it serious thought.
Ending up with a C++(ized) software can take a lot more time and be quite ineffecient.

So if you have some time on your hands ... and this person has reason to stick with you even after picking up new technologies .... Go for It !