I saw a happy user post here Search results with custom tables (owntables) so it’s doable.
Yes, it’s doable. But as explained on
this page, it’s not easy (and takes time) to implement and needs to analyse your request (tables, keys, joins, ...).
If you are interested, send me an email with the requested infos.
The ajaxSearch 1.8.x are deprecated versions. But the search in custom tables, is always possible with the latest 1.9.x releases.
On
this page, you could find an example of an ajaxSearch customization which mixt a filtering search form with custom tables.