Will the non-colluding servers communicate in IT-PIR schemes ? The current literature around Information Theoretic Private Information Retrieval (IT-PIR) schemes assume the existence of multiple copies of the database distributed across non-colluding servers. Much of the research seems to be around the servers not communicating with each other but only with the client. 

Can the results be improved (or are there known results) ? when the the multiple servers communicate among themselves without breaking the security assumptions (say using multiparty computation) ?
When the servers may collude then if they are all corrupted it's exactly the same as 1-server PIR. Thus, in information-theoretic PIR, it is always assumed that only some subset of the servers are corrupted. 

It is unclear to me what you would gain by running MPC between the servers. One possibility is to simulate a single-server PIR with many servers. But this would just cost more.