I have received a response from the translator of the website that venerable Ayya Vimala mentioned on this page.
He prefers status quo, that is, hyperlinks are used on the SuttaCentral website.
He emphasized that he is NOT concerned with copyright issues, rather, it would be his pleasure if his work were useful. However, he is concerned with the accuracy of his translation and problems that may occur because of that. He cannot take responsibility for such problems.
He says he is not a professionally trained Pali translator, and he thinks there are many mistakes in the translations. He feels the quality of his translations is not high enough for publication outside his own website.
He plans to translate Saṃyutta Nikāya in the future, and he is happy the translation to be hyperlinked by SuttaCentral.
He seems to feel uncomfortable that his translation is taken as if an official translation. I think he is just humble about the quality of his translations. However I understand his concern.
I thanked him for his prompt and polite reply, and said to him that I would pass on his message to the SuttaCentral. I also encouraged him to contact me if he changes his mind.
Please let me know if there is something that I can do for you further on this matter.
I am still waiting for the reply from the translator of the other site.
Thank you very much.