I would say it would be difficult.
Monash runs a first year math unit which is considered the methods equivalent. The fail rate was astronomical for what some people consider basic. I know many who failed. I myself only barely made it.
Why? Because methods is a significant leap from further/yr 10 math. You take all these people who haven't done math since year 10 (or in the case of mature aged students at monash, decades) and you give them such a big jump like methods, it will not end well. Another reason is that its two years of hand-holding and being guided through it by an experienced teacher compressed into a semester (12 weeks). I assume unilearn has a roughly similar timeline. You could probably self-teach any VCE course but some would be orders of magnitude harder to do so.
I say this not to discourage you but you asked for an honest assessment, there is mine. You must stay ontop of it and work your butt off. Self-teaching would be rather hard. I assume uni-learn provides study material and a way to ask questions, so, its not really self-teaching, it makes it a bit better.
Keep in mind, if you want to get into a course that needs math, as a general rule, the math will not go away. If you don't like math or lack the aptitude, your years in that course will be hell. That is another thing to consider. If you don't mind math or even enjoy it, there is no issue.