I went to school and uni in Scotland and now teach in a secondary school in England.
You used to do Highers in 5th year (same as year 12) and SYS in 6th year. Usually between 3 and 5 highers in 5th year and then 2 or 3 SYSs and maybe some more highers.
If your SYSs were in the same subjects as you were going to do at uni and your grades were good enough then you could go into 2nd yr (of 4) at a Scottish uni but most people I knew didn't. Most of the English people also went into 1st year and had an easy year along with those who'd done SYSs (I went straight from 5th year with just highers and so actually needed to work in 1st at uni)
Now they do highers and then advanced highers (pretty much the same as SYS) which are equivalent of A2 levels and A levels here. The content won't be exactly the same but then 2 A-level courses offered by 2 exam boards won't have the same content either.
So to answer the original question: 6th yr studies (SYS) are not the same as an A0level but are the equivalent of one.