I checked what unlocks you get for Lt grade 7 and indeed it does say you unlock duty officers but no mention of anythig else. I checked my space abilities and i now have a new ability which is Sensor Scan 1. I assumed that was the reward related to [Mission] Accolade complete: Lieutenent Ability: Rank III but on further checking what rewards you get when you reach Lt grade 8 (which i am still working towards) grade 8 rewards you with the Sensor Scan 1. So now i'm left confused with just what is going on. Information in game seems to be outdated and misleading, not good for new players
"Accolade complete: Lieutenent Ability: Rank III" is a text bug. When you first acquire a Captain ability, regardless of your current rank, it will be Rank I (1). When you advance a rank, your current Captain abilities automatically gain 1 rank. So when you reach Lt. Commander, your Sensor Scan I ability will because Sensor Scan II.
Part of the Free-to-Play game version was changing how level/ranks are displayed. One thing they did was to change the level number by -1. Instead of levels 1-51, they changed it to display as 0-50. The breakpoints that abilities and rewards are given didn't change. So the information you are looking (i.e. Ability at Rank 7 is outdated (aka bugged) and needs to be fixed.
You can report the bug by using the /bug facility. Select "Report a Bag" in the Game Menu. Or type the '/bug' command in the chat window to bring up the Bug reporting window.