Yes, Splunk really doesn't care about the file type. As long as it is a text file and appended to, the forwarder will pick up on the changes.
You may get issues if it is a csv file that is re-written periodically and the beginning of the file has repeating values (like a header row) that would prevent us from detecting whether the file has changed, because we are only looking at the first 256 bytes (by default) to determine whether we have already seen the file before. You may have to play with the initCrcLength setting in inputs.conf.
But it's all guesswork on my end until you tell us more about why you think "it's not working". Your forwarder splunkd.log may give you hints as to what may be going on, too.
