I think adcoms would be dumb not to consider the rigor of an applicant's major and how it correlates to their GPA. So yes, I do think they take that into account when making decisions. However the problem, at least with other professional schools, is the significant pressure on all but the most elite universities to admit students with higher GPAs regardless of their majors.
Why? US News rankings. Their rankings are based largely on "selectivity" which is a composite of class GPA, test scores, and numbers of applicants. This criteria make up to 40% of their total rank IIRC. Whether a school plays this game, and to what extent, is largely an issue of integrity. This applies not only to the difficulty of majors, but to other aspects of an appicants background like extra-curriculars, work experience etc. It's really tempting for universities to pad their classes with a bunch of easy majors that have 4.0 GPAs, rather than having some smart students with 3.0's.
There is a school near where I live that is obsessed with rankings. In the past number of years I watched how they have manipulated (IMO) the statistics of their "selectivity" to make large leaps in their ranking. When you look critically at their stats, they are anomalous, and prove just how far some schools will go to increase their status and the expense of their academics. Kind of an ironic reversal of the "students who are in it only for the grade and not to learn" scenario.