Yes. The divider does not stop the seats reclining and as you say, the size of cabin is variable, I.e. it can be 3 rows (usually the min) or many more.
Yes, reclining in the last row will reduce space for first row of ET but that's the case anywhere, I.e. Reclining in CE will reduce CE space behind you and anyone reclining in ET will reduce space for those in the row behind.