Surely, it does not matter that the employer was not deemed as competent, because it was just training that was being offered, not assessment of competence. If judgement is made on the legality of the situation, how could an external trainer/assessor judge legality - if this was the case, then why do centres not ask for driving licence, waste licence, membership of cps schemes, etc - it would be impossible to judge total legality on what qualifications the boss has.
Provided the candidate has experience, then it is the purpose of the ACS assessment to deem them competent or not. Experience as I understand it, is at the discretion of the centre.
If we had to demark the competence of every employer or apprenticeship mentor, then there would be no apprentices. Full-time students can work for building companies and still come out with their ACS.
Soon we will have all those people with tech-certs taking on apprentices - what do we do then? Tell them they can't do the qualification because their boss isn't qualified.
For a tutor to tell you that your training is worthless is just not playing ball. I would submit a formal complaint and find out the facts about this situation - if they are excluding this for you, then they must include it for everyone else - do they?