Can a company have a Social Media Manager & a Web Content Marketing Manager in different posts? Do they have different tasks or not?

Different tasks, even though both are related to digital media marketing, however, it must be kept in mind that some part of both overlap. At the basic executive level, they need different skills to engage (not too far apart, as both can be learned through experience).

They both are equally important for any organization which is based on e-marketing.

Web content is quite different from social content.

In web content you basically informa about the services and products you are offering whereas in social media in addition to information you will also be providing enough material for continous engagement.

To summ up for any company which is just using online tools for information sharing1 guy will be enough but if company is looking for business through online sites when will definately recommend two different guys for both mediums

I believe it's according to the size of the company it's self if it's big they may need a marketer on social medai , and another on other websites . Though I believe they have a very simillar tasks .

A company can have a Social Media Manager and a Content Manager, they usually won't have a content marketing manager. A social media manager deals with Facebook, Twitter etc from the point of posting, moderation etc and interacting with fans. A content post is more related to preparing editorial and other content for the company's brand (s). Being in content usually requires a special affinity for writing and writing for the web and Internet audiences. 

for a small size company of less than100 workers & company base is not on emarketing exclusively than its one professional job to handle both the operation. depends always how the directors move,,