anybody who considers themselves an anarchist is going to be faced with a barrage of contradictions and conflicts living in this world. how we deal with those contradictions is very individual. we all make compromises, and we (hopefully) choose consciously which ones make the most sense in any given situation.
government is unquestionably one of the major pillars of control and oppression in this world. so is capitalism, but most (all?) of us still participate in that system, however minimally and begrudgingly. it simply isn't an option not to, in many cases. what can be an option is how we choose to do so; in what situations, and to what extent.
if i need a job, and a government job is one that gets me what i need in the easiest way, i would have no problem taking the job. the primary thing that would cause me to reconsider is the extent to which that job serves to strengthen or weaken the institution itself. a gov job that allowed me to potentially weaken the government would be more appealing than many non-gov jobs. a gov job that serves to strengthen the government, or allow it to encroach further into my life (or that of others), would be an easy rejection for me. unless, like dot mentions, that job gave me an opportunity to do shit that could weaken it instead.
there are purists that would disagree, no doubt.