Do aggregate models have the ability to group on long text area Salesforce fields. When trying to group on this specific field, the model is not even showing the field (however, I am able to group on other text fields that are not long text fields) fine. Is this a limitation?
Unsure whether or not you're able to group based on a text field, but inherently I would advise against it. Especially with a long text area, you're going to be looking at a tremendous # of groupings since the input for these fields are very arbitrary.
I would use a picklist to create your groupings as they're much more definitive. Depending on what you're trying to do of course.
If your question more relates to the outputted fields for aggregate tables, you're not going to be able to display grouped information other that the count, count distinct, sum, avg, max, and min of those records.