Sorry this is simply not true.
There are certain oils that are considered contra-indicated with homeopathy, black pepper is one and I seem to remember so is eucalyptus.
Essential oils should not be stored alongside homeopathic remedies.
Most essential oils are perfectly safe to use in conjunction with homeopathy and will not effect the treatment in ANY way. There are a multitude of oils to choose from and only the ones that contra-indicate homeopathy treatments need to be avoided and there are many that can be used instead.
A trained aromatherapist knows which oils not to use it somebody is having homeopathic treatment. A referral or permission from the homeopath is NOT needed. Homeopaths probably know very little about essential oils (I know ours at the Centre knows nothing) so how on earth could they give permission for treatment!