Can the same wildcard SSL certificate be used on different IP addresses and/or boxes?
Yes, there is not technical limitation for this; except if your CA prohibits this use explicitly.
The most frequently limitation given by a CA is on the "physical servers", but may be someone limits even on IP basis.
As an example, Geotrust Wildcard Ssl says:
If you need to span the wildcard certificate across multiple physical servers, you may purchase additional licenses.