Sometimes, vocation directors will take candidates from outside the diocese, but it varies. I think it is a case-by-case basis, and some dioceses will not take men over a certain age. I knew a few people (mostly later vocations) that did the pre-theologate at Ave Maria University in Florida or paid their own way for pre-theology at Holy Apostles in Connecticut and were picked up by a diocese before going to major seminary.
Most dioceses do want a candidate to live in the diocese for a little while beforehand. I've heard that the Archdiocese of Washington DC is an exception, because Washington DC does not have a lot of long-term residents (i.e. people migrate to DC for work or school, and may stay there a few years before moving to another place for another job).
I know several dioceses are in need of priests. Fortunately, some dioces have really come up in vocations due to the efforts of a newer bishop. Cleveland, Fort Worth, Dallas, Saginaw, Houston (in my opinion anyway), Charlotte, Charleston (thank you Bishop Baker), and Raleigh are all good examples of this within the last 10 years (since 2004). I also know that Bishop Kelleher of the Archdiocese of Kansas City between 1993 and 2003 increased vocations from 3 to 21 during his tenure, and many of these men were "home grown".
While I still think Peoria, Rockford, and Lincoln are still saying "what priest shortage?" I know Arlington (Virginia) has not had as many seminarians as it had when Bishop Keating was the local ordinary (Keating died in 1999) and Fr. James Gould was the vocations director.
As far as incardination, that is fairly common. I don't know the details of how that all works, but in recent years, a few priests I know have left the Legionaires of Christ and been incardinated (or are working on being incardinated) into a diocese. One is Fr. Jonathan Morris (who is on Fox News frequently), who has been incardinated into the Archdiocese of New York. There is also a priest from the LC who is in the process of being incardinated into my diocese. I also know of personally a few former Jesuits who left the order and have been incardinated into a diocese, such as Austin, and I am familiar with at least two Vincentians (now deceased) who were incardinated into the Dallas Diocese.
Thanks for asking these questions. They are good ones.