Do you think its illegal to promote affiliate products by offering non-monetary bonus offers such as ebooks,etc?
Lol what do you mean ? Of course it is not illegal as long as you are offering ebooks that you have rights to offer. But don't be crazy giving out some one else ebook which you hold no rights to give.
Not unless the affilate program prohibits this expressly. I have seen many websites offering free extra bonuses [Non-monetary] if affiliate products are bought through that website.