Should I duplicate the value of a related Model in the other Model for indexing with Sphinx?

If I have a model named Entries and a HMABT relationship with another
model Tags, and I use Sphynx for searching models by their tags, would
it be convenient to save the tags name into the Entries table each time
an Entrie is saved, and tell Sphinx to index Entries instead of Tags?

Also, the Tags would have an alias_of/synonym_of column, and it would
search for synonyms before it sends the keywords to Sphinx

Should I use this approach? What recommendations would you give me? ^^