Of course that the interference pattern disappears whether or not you are aware of the experimenter who has bombarded the electrons with other particles.
The quantum mechanical predictions are surely independent of the "consciousness" of the other objects, which is what may lead some people to the same question as yours. Quantum mechanics is valid for predictions of any observed phenomena, whether they incorporate macroscopic objects and humans or not.
The electron is being entangled with some additional particles (photons?) that someone uses to bombard the electrons. These photons won't be detected again. We will only observe electrons, so it's enough to describe them by the density matrix for electrons only. Mathematically:
$$ |\psi\rangle = a |{\rm left}\rangle + b |{\rm right}\rangle \to a |{\rm left}\rangle \otimes |{\rm left\,\,photons}\rangle + b |{\rm right}\rangle \otimes |{\rm right\,\,photons}\rangle $$
and
$$ |\psi\rangle \to \rho ={\rm Tr}_{\rm partial\,\,over\,\,photons} |\psi\rangle \langle \psi| = |a|^2 |{\rm left}\rangle \langle {\rm left}| + |b|^2 |{\rm right}\rangle \langle {\rm right}| $$
That's why we're allowed to trace the density matrix over the photons' Hilbert space, and by doing so, the information about the relative phase of the left-slit and right-slit portions of the electron's wave function disappears (because these two portions are entangled with different, orthogonal wave functions of the photons) which is why interference is not possible anymore.
So the interference pattern disappears even if no one else is observing the reflected photons at all.
Where quantum mechanics "requires" consciousness or active knowledge is when you ask whom the predictions of QM are made for. They're not made for an objective world: at the fundamental level, none exists. Predictions of QM are meant to be used by a "conscious observer" who may observe the actual outcomes of experiments – whose probabilities are calculated as expectation values of the projection operators corresponding to the Yes/No questions.
But once you are such an observer, you may treat all objects in the world on par – as blind systems of particles that universally obey the laws of quantum mechanics. Their "humanity" or "knowledge" or "plan to exploit an observation" or "consciousness" is totally irrelevant for your predictions and their verification.
The real "paradox" about an observer knowing about another observer is that observer A may observe observer B who observes system S. According to B, the outcomes of measurements are known as long as B "perceives" them. However, A may evolve B+S into Schrödinger cat-like superpositions and only "collapse them" i.e. interpret them once A perceives his observations. So A,B may disagree when "facts became facts". But this question "when a fact became a fact" isn't measurable: any observer may "delay" this moment up to the moment when he actually perceives the outcomes, and there won't be any contradictions in the final perceptions of A,B. (Of course, A may also uniquely calculate the earlier moment when B says "now I know the result": this moment is before A observes the situation, and it is earlier because it's independent on the actual outcome that B perceives. However, B is still just a part of the physical dull world for A.)
