If you have created dictionaries with search terms, you call up a word frequeny analysis for only these words.
Click on the label Word Frequencies in the MAXDictio menu tab (not on the icon) and select Word Frequencies (Only Words From Dictionary) from the drop-down menu. The following dialog window will appear, which essentially corresponds to the standard dialog for word frequencies:

The options are described in the section on Word Frequencies, however neither lemmatization nor stop word lists can be used.
The count begins as soon as you click on OK. The results table naturally contains only dictionary words.