At first let me point you to the difference between SS and Waffen-SS. Assuming you want to know about the Waffen-SS, then yes there are many recorded and known instances where units were "attached" to a regular army group. For example LSAH fought in '41 in the 12th Army and were subordinated to the army commander, but usually not at the divisional but rather army level. They were at least at the beginning viewed as a kind of elite and received better equipment and would be used by the army commander at the schwerpunkt.

To your second question, yes an officer was an officer and a nco a nco. They were under standard military discipline and the ranks used the same system, so silver stars for officers, gold stars for nco's and stripes/chevrons for enlisted.