Yes, you can include arbitrary data sets in the choices sheet and query them. Currently the XLSForm support for that is not so good so the structure is a bit odd. This form shows the approach. You can read the comments for explanations. There's also another example I described at Progress out of Poverty Index (PPI) tools - #14 by LN.
search() and pulldata() let you pull values from arbitrary CSVs but I don't personally use those because they're not part of the official specification. You may want to read more at http://xlsform.org/en/#dynamic-selects-from-pre-loaded-data.