The article Djokovic looking over his shoulder in battle for No. 1, which is published directly on the ATP tour website, mentions that:
The 27-year-old Djokovic has a slender 490-point lead over Federer in the Emirates ATP Race To London going into Paris. There is a potential total of 2,500 points to be earned in Paris and at the Barclays ATP World Tour Finals, with Federer also having the chance to earn possibly decisive points when he leads Switzerland in the Davis Cup final against France. The Basel native is looking to become the oldest year-end No. 1 by some margin. Previously, Ivan Lendl and Andre Agassi both achieved the feat when they were 29.
To prevent link rot, I will also add a link to the version of this article on Wayback Machine.
Since I was not able to find anything about this in faq or rulebook, this article published directly on the ATP website is the closest thing to official standpoint of ATP I was able to find.
As already menioned in a comment I was able to find some other sources which say that DC finals can be a factor for Year-End No. 1. (Of course, any unofficial source can contain mistakes.) For example: 1, 2, 3,
11. (Some of the sources I link there are internet discussions, some of them are blogs or articles. You'll have to decide for yourself to which extent you consider them reliable.)
I should clarify that I was able to find in the 2014 ATP Rulebook (internet archive) several things that are determined from the ranking after World Tour Finals (bonus pool) or even before WTF (commited players). But I did not find a mention of year-end no. 1.
I will copy here some parts from Chapter 1, which are relevant to this these topics:
I. ATP CIRCUIT REGULATIONS
C. Commitment Player
A 2014 ATP commitment player is any player positioned in the Top 30 in the ATP 2013
Rankings (singles) as of November 4, 2013.
... 2014 Davis Cup points may be counted as one (1) of the best of six (6)
in the Emirates ATP Rankings, however, it shall not count towards the commitment
requirement of a commitment player. ...
G. ATP World Tour Masters 1000 & Barclays ATP World Tour Finals (“WTF”) Bonus
Players in good standing shall be eligible for the bonus pool based upon the Emirates
ATP Rankings as of the Monday following the Barclays ATP World Tour Finals in the