In my version of RM2 (last 2.6) there is no "/dev/fb0" in the /proc/$pid/maps but there is a "/dev/shm/swtfb.01"
That looks like rm2 fb shime. That might have change due to the update.
I'll try with this change and report

I tried the following

pid=$(pidof xochitl)
offset=$(grep "/dev/shm/swtfb.01" /proc/$pid/maps | awk -F '-' '{print substr($2, 0, 8)}')
dd if=/proc/$pid/mem bs=1 count=2628288 skip=$((0x$offset + 8)) 2>/dev/null > raw
gm convert -depth 8 -size 1872x1404+0 gray:raw out.pdf

Well the output pdf is ugly and nothing close to the fb right now ...