Hi
Short answer: no, there isn't a search option to search the whole of an LO.
Longer answer:
Xerte loads each page dynamically as you visit each page so it's not a trivial thing to build whole LO search. That said because in most cases text is text in Xerte you can use the browser Ctrl + F to search individual pages and that can be quite useful on long bootstrap project pages for instance.
Both XOT and Bootstrap projects also have glossary options and you could build your own menu of page links based on the text someone might search for and then if someone uses ctrl + x to search for that term they will hit the page link and be able to navigated to that page.
HTH
Ron