Connecting two SLA batteries of different but close capacity in series
Yes, this is still dangerous and will damage/destroy the lower-capacity battery by reverse-charging if it's discharged too far. As long as the voltage of the lower-capacity battery doesn't go below its normal end-of-discharge voltage (about 5.2V or so), it'll work fine.

However, if you just let it discharge without a low-voltage cutoff (or manual supervision), bad things will happen.