Oh, a nice idiomatic phrase. I like it. Could it, however, mean a somewhat weird question "Can we count with you?"?
Why isn't it "Můžeme na vás počítat?"? Or "Můžeme na vás spolehnout?"
the course simply does not include "spolehnout (se)".
"počítat na vás" does not mean anything if "vás" is accusative and means something physically odd if it is locative. like you are doing counting while being on top of someone.