Do neutered domestic cats hump and get boners?

Yes and yes is the response. Neutering of male cats removes the testes. This removes the organ that produces testosterone. How do they feel emotionally going forward? I did an article about how a man feels when castrated to try and get inside the head of a cat. Click here if you'd like to read it.

Do neutered domestic cats hump and get boners? Yes and Yes.

Testosterone is not the only trigger or motivator for a feline's desire to have sex. It is a complex interaction of psychological, neural, vascular, and endocrine (hormone) factors, and is associated with sexual arousal. 

I guess that losing the ability to create one important hormone, testosterone, is not enough to stop a male cat's desire to hump and get an erection. But this be a personality issue too. It'll depend on the individual cat.

My male cat humps my arm when it is in a fleece dressing gown. He loves it and it substitutes having sex with a female cat. He was neutered when very young as is normal for rescue domestic cats.

He is also still territorial. He is still an aggressor to other cats who he likes to boss around. 

Some commenters say that cats gradually get used to not having testosterone in their bodies and will stop humping about 12 weeks after the operation.

This has not happened for my cat. He was neutered 5.5 years ago and he still humps my arm daily. It is as regular as that. Something more than testosterone is driving it.

Some say that when male cats are neutered at an older age they don't lose the desire to hump. Not so for me and my cat. As mentioned he was neutered at the earliest opportunity as directed by the cat rescue. This is about 8 weeks old.