Alguém chama Sam Samwise?

Sim, "Samwise" é usado em vários lugares. É usado principalmente de maneira formal para enfatizar algo (por Frodo), ou por pessoas adequadamente formais que usariam o primeiro nome - Faramir e seus homens.

Alguns exemplos:

"I don't know how long we shall take to – to finish," said Frodo. "We were miserably delayed in the hills. But Samwise Gamgee, my dear hobbit – indeed, Sam my dearest hobbit, friend of friends – I do not think we need give thought to what comes after that."

E quando se encontrar com Faramir e seus homens:

"Frodo son of Drogo is my name, and with me is Samwise son of Hamfast, a worthy hobbit in my service."

...

Mablung laughed. "I do not think the Captain will leave you here, Master Samwise," he said. "But you shall see."

...

"Now you, Frodo and Samwise, will come with me and my guards," said Faramir.

Existem muitos outros exemplos, enquanto Frodo e Sam estão com Faramir em Ithilien.

A primeira ocorrência que encontrei em The Two Towers capítulo 2:

'I don’t know how long we shall take to – to finish,’ said Frodo. ‘We were miserably delayed in the hills. But Samwise Gamgee, my dear hobbit – indeed, Sam my dearest hobbit, friend of friends – I do not think we need give thought to what comes after that. To do the job as you put it – what hope is there that we ever shall? And if we do, who knows what will come of that? If the One goes into the Fire, and we are at hand? I ask you, Sam, are we ever likely to need bread again? I think not. If we can nurse our limbs to bring us to Mount Doom, that is all we can do. More than I can, I begin to feel.’

Sam não é chamado de "Samwise" com muita frequência, mas ocorre regularmente no segundo e terceiro livros, mas estranhamente não no primeiro livro.

Sim, por exemplo, você está esquecendo o famoso 'Samwise the brave', que está no livro como 'Samwise the stouthearted' e inúmeras outras ocorrências.