Is there a difference between active Army Reservists and Active duty Officers?

They are completely different personnel systems. Promotions, assignments, everything. Also, AGR isn't something you join like joining the AD. For AGR, you have to be a reservists and then apply to an open position. Just like any other federal or state job, there are other people competing and competition can be stiff. The activation is for a limited time period, usually three years, you can often reapply to continue in that role.

The majority of company grade officers and a smaller percentage of junior (04) field grade officers in the regular armed forces are reserve officers serving their initial commitment dependent upon the program they are in, i.e. a pilot will have a longer training period and active duty commitment than an infantry or supply officer. Once the reserve officer has fulfilled their initial obligation, they can then become an active (drilling) reservist by affiliating with a specific deployable reserve unit, or are assigned to the Individual Ready Reserve (IRR) that consists of persons who have fulfilled their active commitment, but are not in a drilling unit and are still eligible to recall and mobilization on an individual basis. Both drilling reservists and IRR reservists are eligible to apply for full time positions in support of the reserve community, but these positions are limited and extremely competitive. Reservists still serving their initial active duty commitment compete for promotion with their active duty contemporaries. Officers in drilling units, or on active duty in support of the reserves compete for promotion separately from those on active duty in the regular forces. Both regular and reserve officers are commissioned, but hold those commissions as regular or reserve officers. I am not qualified to comment on the guard community.

One is commissioned, one is not.

Are your referring to Active Guard Reserve (AGR) or being a drilling reservist?