In Souls of Black Folks, is "within the Veil" used to indicate being "black folk" and "without" being white folk, as it also is a mask between them?

In brief, yes, in W. E. Burghardt Du Bois’s
Souls of Black Folk, "within the Veil" refers
to the world of "black folk" and "without the Veil" refers to the world of white folk.
In "The Forethought," Du Bois speaks of the two worlds "within and without the Veil."
Then he very carefully defines, in poetic terms, the worlds within and without. He says
that he "leaves the white world" and that he steps "within the Veil,"which is the
antithesis, or the world of black folk. He goes on to say that the reason he does this
is so that the "Gentle Reader," the white reader, might see the "deeper recesses" within
the Veil: "its religion, the passion of its human sorrow, and the struggle of its
greater souls." In this description, "its" represents a metonymy in which Veil now
stands for the lives of black folk who dwell their whole lives within the Veil. To make
matters even more certain, Du Bois adds at the end of "The Forethought" a most poetic
and poignant self-identification that positions his own life precisely within the Veil:

need I add
that I who speak here am bone of the bone and flesh of the flesh of them that live
within the Veil?

Yet Du Bois'
use of this symbol is far more complex than that, making it all that much more confusing
to understand if you are not alert in following his poetic prose. In Chapter 1, he
defines the veil itself by describing his first instance of recognizing the divide that
separates him and his folk from white folk with "stringy heads." He describes that "it
dawned upon me with a certain suddenness that I was different from the others." He
explains that he was "shut out from their world by a vast veil." He also says he felt
contempt for those white folk on the other side of the veil. So we now we have two
meanings to veil. The first is "the Veil" that contains the souls of black folks "within
the Veil" and the second is "the veil" that separates black folk, who are like white
folk "in heart and life and longing," and leaves them "shut out from their world by a
vast veil."

There are two other uses for "veil" in the
first three chapters. One is the idiomatic expression "born with a veil," which refers
to a condition at birth in which a thin membrane veil covers the face of the new born.
In Du Bois’ allusion to it, this veil refers to an ability in psychic powers. We can
confirm this because "born with a veil" is used in conjunction with "seventh son,"
another idiomatic expression that may mean a son born with special powers. Du Bois links
these special powers to psychic abilities with yet another idiomatic expression, "second
sight," which refers to clairvoyance, a psychic ability that Du Bois has thus attributed
to black folk within the Veil..

The third use for "veil" is
in Chapter 2. Du Bois constructs a powerful metaphor comparing a land "right merry with
the sun" to a "figure veiled and bowed" in the "King's Highways." America of white folks
is the land where "children sing" and the unembraced black folks of the "color-line" is
the figure draped in a veil of shame or mourning sitting in the midst of plenty, bowed
down and with nothing but the veil.

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I have seen a land right merry with the sun,
where children sing, and rolling hills lie like passioned women wanton with harvest. And
there in the King's Highways sat and sits a figure veiled and bowed, by which the
traveller's footsteps hasten as they go. ... the problem of the
color-line.