yes, you can get it at same time as employment leave
you will get it taxed by your employer as if it is an extension of your normal pay from them and will tax it at the applicable rate for your combined payment as if all from your employer. this is the reason that the payment is delivered by employer, to make sure you are correctly taxed...

as long as you don't return to work (which it sounds like you won't if you're taking 6 months off!) before the 18 week payment period is done, you're all good.