What's possible and what's practical are two different things here. This knowledge base article: http://help.filemaker.com/app/answers/detail/a_id/7541
Suggests that this will work if the text is broken up into words and not a continuous string of nonblank characters. It will, however result in a very large index on the field.
You may want to download the 30 day free trial, import some data into it and see how well it performs.