The word 'ego' can most definitely be used as spuk. As funkyanarchy stated in their comment, it depends on how the word is used. And again, as funky@ alluded, Stirner's term, der Einzige, is not best translatable as 'the ego' (although he did use the term 'ego' throughout his text) but as 'the unique.'
How can 'ego' be used as spuk and why is der einzige not such? First, let's look at der einzige.
That der einzige=spook is an old criticism used against Stirner. The ink had barely dried after _Der Einzige und sein Eigentum_ was penned when this charge was leveled against him. However, in _Stirner's Critics_ (which I think is better read prior to reading Der Einzige) Stirner makes it very clear that language may only point toward, indicate, where he's attempting to take us (the reader) and that this where is ineffable, inconceivable unspeakable:
"Stirner names the unique and says at the same time that 'names don't name it.'"
"What Stirner says is a word, a thought, a concept; what Stirner means is neither a word, nor thought, nor concept. What he says is not the meaning, what he means cannot be said."
Notice that Stirner self-refers in the third-person. Der einzige may (perhaps) be best referred to as no-thing. Der einzige isn't an object, nor can 'it' be an instance of what Whitehead called 'misplaced concreteness,' a long-winded, but illustrative, way of saying 'reification' or 'spook.'
I try to place einzige as a where, rather than attempt to visualize or define a what (an 'object') when speaking and writing about der einzige. Places are always qualified; undefinable although describable; relational; living/'organic'; moving; and messy. (Perhaps this last descriptor points toward a major motivation of Western thought turning toward a unified, three dimensional conceptualization of the world we regularly refer to as 'space.' It renders the world dead and silent in order for the scientic autopsy to begin, as Hillman put it. Another story for another time.)
A couple of remarks about how 'ego' may become spooky.
At its most simple, it's just another case of 'thingifying' that which is no-thing, not-an-object. Various illustrations may help:
Continuing the place-language from above it's a case of taking the proverbial map to be the territory.
It's confusing a grunt we monkeys make for that which that grunt indicates, figuratively points toward, which we believe to be equal, equatable; a perpetual/perpetuating belief in what Nietzsche called 'the soul-concept.' A belief in 'essences' extricable by 'the mind' through 'reason' from the 'mere appearance' before us (scare quotes are most definitely intended here).
Another: 'Narcissism' is the conceptualization/abstraction/thingification of 'self' whereas where Stirner was pointing us through the language of der einzige cannot be imagined at all.