Are EU representatives involved in advising companies on GDPR compliance in any regard?

It’s certainly possible. The representative can provide additional or ancillary services on top of the bare representation. And, if a contact is received from a data subject, it may well be that the business could look to the representative to assist it in dealing with GDPR compliance issues in respect of that contact. So, the core function of the representative is simply to provide that point of contact and liaison between local subjects and supervisory authorities in the business, but there is nothing to prevent the representative being able to provide additional or ancillary services around GDPR compliance, as they arise.