I've had a client bring their own blend and I have no hesitation using it. If there's a proven track record of no reaction then go ahead and make sure you note this on their file.
With regards to mobile work and blended oils. I have 4 different blends that I make myself. My kit comprises of the following:
Jet Lag - peppermint, cardamom and rosemary (contra for epilepsy)
Relaxing - lavender, geranium, frankincense and vetiver
Preg/mild relax - orange, petitgrain and neroli
Muscle - lemongrass, french marjoram and black pepper
Tiger Balm for those extra tense areas
Plain base oil of sunflower oil
Bear in mind that I'm trained Aromatherapist and have been using these blends for over 10yrs.
Cheers, Sue