Well, Total Commander
has very good search capabilities. With TC you can search for files with size less than xx bytes and does NOT contain a specified text. The specified text can be also a Perl regular expression. So with Total Commander you will easily get the list of files you want.
To do this with UltraEdit needs much of work.
First you must get a list of all files in your directories. This can be done since UE v9.10 with a Find In Files with an empty search string with results to an edit window.
Next you have to run on same files a regular expression search to find the files which contain words with at least x characters. This is also a Find In Files search with results to an edit window. From this result you have to delete everything except the file names with full path and sort the file with removing duplicate file names because a word is surely found more than once in a file. I have posted already a macro which does this job - macro depends on your version of UltraEdit.
Now you have 2 lists with file names: First list contains all files and second list contains all files with at least 1 word (or more - depends on your macro which evaluates the search result) which has at least x characters.
You can now remove with a macro all file names from list 2 in the list of file 1 and the result should be a list of files which does not have (enough) words.