I have a question regarding the above.
Here is the answer, below.
On a more serious note:
If during the research and translation work on a project for an agency or colllegue Translator subcontracting me I get the impression it might be in doubt that the end customer has the legal rights to have a document translated, what should be the consequences?
You should not translate anything that contributes directly or fairly directly to crime (where "crime" is defined by your country's laws or by your own moral values). If you're a member of a translators' association, its code of ethics might include dishonesty or various forms of moral decay as well.
Am I protected by the fact that I am only delivering translation services and that my T&C´s listed in the invoice issued to my contracting entity state that I should be kept free of any harm by claims from third parties?
I doubt if an anti-claim-harm clause will save you, but perhaps common sense might, although IANAL. Usually, anyone may create or pay for a translation of anything, as long as the translation is used in accordance to fair use or fair usage. Beyond that, a license is required from the author of the original text (and from the translator, although that is rarely said).
My big question to you is what kind of proof you would accept if you were to confront your client and he would submit proof to you that everythingn is in fact legit. What sort of proof would you consider acceptable proof?