They were certainly allowed visitors, though it needs a stretch of the imagination to see that things were very different then. Visiting was very restricted, perhaps just one afternoon a week, sometimes a month, usually on a Saturday or Sunday. Most asylums were well away from towns, and patients often placed somewhere inconvenient to friends or family; cars were the property of the rich, so visitors depended on public transport, journeys were long, and it meant giving up the only day they might have off work during the week. Many families regarded placement in an institution as shameful and were not keen to visit at the best of times. There were few social workers, no support for families or 'care in the community,' and there were thousands of men and women who lived out their lives in asylums when today they would have been living in the community. Then, there was no 'care in the community,' no half-way houses or local residential accommodation, few social workers and no support for families. By the time men were fit for discharge, there was usually nowhere for them to go, and no-one willing to take responsibility for their discharge. In addition, many patients felt fairly safe and secure in an environment that had been their home for years/decades - who would have helped them re-adjust to the outside world? I doubt if many of these men would have been a danger to others though - it was they themselves who were at risk - the outside world didn't know how to cope with them.
My own brother entered an institution of this type in 1944, though not through war trauma. The hospital was in a rural location, more than two hours drive away from our home, and as my parents didn't have a car visits were usually just two or three times a year. Lack of visits were not always through choice - my mother said many years later that she was desperate to see him, but just couldn't cope with the trauma of visits and goodbyes, and my father was ashamed of him. He was there for almost forty years until changes in 'care in the community' in the 1980s meant that he was moved to a small, residential home in the middle of a large town where he still lives and has a fuller life than most elderly men. We take these things for granted now, but need to be thankful for a more caring, enlightened society.
Sue