I'd expect that they're sending people to become familiar with the places and do the preliminary on-the-ground coordination.

or fact-finding or get-acquainted trip

Under some circumstances, a fact-finding or informational trip may be accepted from a private organization by a City officer or employee in the exercise of ...
www.honolulu.gov/ethics/travel.htm

Examples of ‘Vorreisen’ on google seem to suggest optional add-ons at the start of the holiday (as opposed to ‘Verlängerungen’ at the end), e.g.
Vorreisen und Verlängerungen für unsere Mekong-Flusskreuzfahrt „Orchidee“:
Für die Mekong-Flusskreuzfahrt bieten wir fakultativ Vorreisen in Thailand (Bangkok & River Kwai) oder China (Provinz Yunnan) bzw. ein fünftägiges Verlängerungsprogramm zu den weltberühmten Tempeln von Angkor (Kambodscha) an. Zu Einzelheiten beraten und informieren wir Sie gern.
http://www.eastasiatours.de/397485.0.html

IMO suggesting that anyone is checking out the destination may be reading too much into this minimal context. A safer option might be to opt for a non-committal ‘preliminary’ to translate the prefix ‘Vor-‘.
This could even be taken to include the interpretations already given.

In logistics, a "Vorreise" is a synonym of "Vorlauf" and refers to transportation from the source to the ship or airplane that will take the products or goods to their desination.

Since you have basically no firm context, there's no way to know for sure (making Andrew's suggestion a very strong option), but in the event that they are talking about getting the various goods for planned events sent to a central place for shipping/dispatch to the final destination, perhaps the logistics sense is in fact right.

This Web site (http://www.tis-gdv.de/tis/taz/v/vorlauf.htm) uses "pre-carriage," which is very British. SAP uses "preliminary leg," which is similar to Andrew's solution.