The answer to your question, as it is to most good questions, is a strong, solid yes-and-no. The answer requires putting human castration into its historical and cultural context.
At its simplest end, we need to consider the prevalence and acceptance of pain before the invention of modern anesthesia. Remember that major limb amputations (arms & legs) were done without any painkillers up until fairly recent times. (And still are when the medical system breaks down as it has in Iraq today.) There was also an acceptance of a death rate from surgery that would receive criminal prosecution today.
We also need to consider who were the recipients of the surgery. In the earliest period it was slaves, who were considered essentially equivalent to domestic animals - it's no big deal if you loose one now and then. It's figured into the increased value of the rest of the now castrated stock. Later there were followers of various religions (the Mother Goddess, some early Christians, etc.) Death as a consequence of a religious act was culturally acceptable.
Early Chinese eunuchs were mostly recruited from conquered border peoples. Another, smaller, source was convicted criminals. Usually it was not the convicted criminal himself. He was executed and his sons castrated, and for very serious crimes, his brothers and nephews as well. The only mortality statistic I have is from the early Ming, when 329 of 1,565 Hmong boys died after castration when the Chinese army conquered their territory. This is a death rate of over 20%! Only later were there "voluntary" eunuchs in China. There wasn't enough external conquest to provide sufficient eunuchs for the court. By then, there were also "experts" attached to the palace to perform the surgery and opium and topical anesthesia were in use. The death rate was still about 3 to 5 percent according to G.C.Stent, who interviewed both eunuchs and surgeons in the 1890s. Pain and suffering and surgical complications are uncounted.
In the west, the castration of younger sons in Byzantine families in order to fit them for religious and government posts, was done by trained surgeons. I have found NO information on death rates as the operation was illegal, though common. Neither have I found information on the death rates in western Europe for the production of castrati, though, again, the surgery was often performed by trained surgeons - even though it was illegal everywhere. It is even said that one hospital in Florence reserved eight beds for young boys recuperating from castrations. That there were deaths IS reported.
The statistics on death rate in sub-Saharan Africa are so unreliable as to not bare repeating. They were mostly used as horror stories by early anti-slavery activists and are mostly higher than the increased value of the slaves would allow - total value of the new eunuchs would be less than the value of the boys before castration! The slave traders were businessmen and these figures must be wrong.
I've been involved with enough animal castration to know that I would consider the consequences of the same techniques used on humans to be absolutely unacceptable today. Fantasy is fine. Reality is very different.
I recently posted a page from a livestock supply catalog, listing a variety of animal castration tools:
http://www.eunuch.org/vbulletin/showthr ... eadid=3173 As I noted there, I've used some of them on cattle, sheep, and goats. There's NO WAY that I would consider doing the same with my dog. I care too much about him. The only way for him would be in a sterile environment with modern anesthesia, a trained surgeon/veterinarian, and follow-up with pain-killers and antibiotics. Even then, there are possible complications. Some of the Archive members can attest to personal experience with them and have done so.