hi.
i use skype 6.21 with nvda 2015.4 and i dont have any problem.
if you check accessibility in skype settings, skype works well with
nvda and you dont need to install any addons or other programs to make
it accessible for nvda.
and also skype is better supported if you install skype version 7 and
nvda has many keys to supports it better.
God bless you.

--
Those who follow the Messenger-Prophet, the Ummi, whom they find
written down with them in the Taurat and the Injeel [who] enjoins them
good and forbids them evil, and makes lawful to them the good things
and makes unlawful to them impure things, and removes from them their
burden and the shackles which were upon them; so [as for] those who
believe in him and honor him and help him, and follow the light which
has been sent down with him, these it is that are the successful.
holy quran, chapter 7, verse 157.
best website for studying islamic book in different languages
al-islam.org