Because HR is limited to verifying only the information in the letter (ie length of employment, wage, position) lenders have to use these other techniques such as the reverse lookup and canada 411 to verify that the company name and phone number match. This is not always the case however.
Normally, HR within large reputable companies would not comment on more generic questions such as work ethic, or if they would rent to them as they may not even know the individual and those are personal opinions.
You may well be getting a more legitimate employment verification if the employer is not answering those questions.......
Hope that helps,