Sorry for the late reply. I only just checked back on this thread.
To answer your question it should be fine. Just make sure that you use the same number of columns for each table. You may want to specify the columns like this:
In the example above the column names may be different and not exist in all of the tables, but the review_date does exist in all of the tables. If review_date did not exist in all three tables it would still sort it based on the tables that do have review_date, but the other tables may be sorted a little oddly. Try making sure that the number of columns specified for each table is the same. For now try to avoid using * to specify all columns and write out the ones you want making sure that the same number of columns is listed for each table.
(SELECT ID, title, review_date, va_english FROM table1)
(SELECT ID, title, review_date, artwork FROM table2)
(SELECT ID, title, review_date, author title FROM table3)
ORDER BY review_date DESC LIMIT 900
If you are still having trouble try posting the error message you are getting and the query you are using.