No, it is not true that osteopathy courses in the UK only include manipulative techniques and do not include cranial and visceral techniques. However what is true is that the courses offered by different institutions offer different proportions of these techniques. For a list of accredited courses see
www.osteopathy.org.uk/car...ourses.php
I qualified from the BSO, where the proportion of cranial/visceral techniques taught on the undergraduate course is low compared to the proportion of manipulative techniques. Other providers, for example the ESO, teach more cranial/visceral at undergraduate level.
It is a matter of opinion whether these very powerful techniques are best taught at undergraduate level, or later on when you have acquired the osteopathic experience and palpatry literacy to be able to make full use of them.