DOM in relative clauses

It is well know that Spanish exhibits Differential Object Marking (DOM), that is, some objects (in general, [+specific] and [+animate] objects) are marked with a preposition:

(1) Juan besó a la mujer

In (1), the preposition is mandatory. However, this effect seems to disappear with objects that are relativized:

(2) La mujer que Juan besó

However, if the relative pronoun is “quien” (that is, “who”, which is marked [+human]) the preposition is mandatory:

(3) La mujer a quien Juan besó

Interesting, the preposition is mandatory too if the relative pronoun gets a determiner:

(4) La mujer a la que Juan besó

This is true even if the nominal is non human:

(5) La gata a la que alimentaste

Notice that in these cases the relative clause is still restrictive. In fact, inanimate nominals (that cannot receive preposition in full clauses) cannot be relativized by using a determiner (at least the relative clause is interpreted non-restrictively):

(6) * La casa la que construiste [restrictive]
(7) La casa, la que construiste [non restrictive]

Can we take advantage if this to explore the structure of relative clauses, in particular, can we test if the relativized object is raised or base-generated using these contrasts?