I asked in IRC and it is not possible with tracker-search-tool but it is possible on the CLI:

The tracker search tool is pretty simple (and I am not very familiar
with it) but at the least this can be
done using command line tools (or
custom queries in general). For instance, to find all
the images under a specific directory
(or actually the url of which starts
with that specific directory) that
Full-Text-Search match the string
testi can be obtained with

tracker-sparql -q "SELECT ?uri nfo:fileName(?uri) WHERE {?uri a nfo:Image . ?uri fts:match 'testi' . ?uri nie:url ?url FILTER(fn:starts-with(?url, 'file:///home/masi/Pictures/Wallpapers')) }"