Capital ships as flagship platforms

Were dreadnought-era capital ships built with facilities for visiting dignitaries?

Yes; their intended flagship role included facilities suitable for senior visitors and official hosting.

Dreadnought-era capital ships were intended to be capable of serving as flagships. That command role required facilities beyond the needs of an ordinary ship's company. The same spaces could receive senior visitors and dignitaries. Ceremonial accommodation was therefore an extension of the ship's operational command function.