Single people at monastery on Mt Koya?

I was informed by Japan guest houses that ryokans dont like taking reservations from single people.
Surely a shibuko is not classified as a ryokan. Is this normal practice? As I am a practicing Buddhist I would really love to visit Mt Koya.
Does anyone have recommendations please

Have you actually tried to make a reservation and been rejected because you're one person? Certainly sometimes ryokan (especially during the busiest seasons) don't allow or charge extra for single guests, because they take a room that can hold 2-4 people usually. But it depends a lot on each individual place and season. Try making your reservation first and see how it goes.

The shukubo in Koyasan operate very much like ryokan, and I'm not sure but they might even belong to the ryokan or minsuku associations. I spot checked a few of their reservation sites and at least one allowed single reservations via their online systems. The rest didn't have good online systems or were too vague to tell if it was ok. So I'd echo scarreddragon's advice and try contacting some of the shukubo directly to see what they say. You can find more info here:

http://www.japan-guide.com/e/e4905.html

Try making a reservation via Japanican or Booking.com. I did it last time and many of them accepted a solo traveler.

Nuj

I stay at Daishin-in Zen shukubo right in Kyoto often. It takes a single (5,000yen including 500yen bf) and the dinner is optional so I usually have Shojin Ryori (5,000yen & up) one night and eat out other nights. It is located in the Myoshinji temple complex, the same as Shunko-in and has the morning prayer called Otsutome at 6am. It is very popular with single woman and Europeans visiting Kyoto and Arashiyama and walkable to Ryoanji, Kinkakuji, etc. through off beaten path. The tranquil off-beaten Myoshinji complex has Taizo-in which is a better option than Ryoanji, IMO, with beautiful garden, koi pond(you can feed them) and Ying-Yang rock gardens.

I was able to stay at Henjoko-in Temple just after Golden Week in 2013. I had no trouble booking a single.

I stayed at the Ekoin on Koyasan as a solo traveller a few years ago with no problem. I met a few other solo travellers and we braved the Okunoin cemetary together at night, and chatted in the common room. I'd say it's quite common for solo travellers to book temple lodgings on Koyasan.