How can I unarchive this?
"this" being Versus #7? There's a free reimplementation of LhA for Linux, it's called lhasa. Just check if your distribution has a package with that name (Debian does). It extracts vs7-ami.lha just fine.
There's also a (not completely free) port of LhA, some distributions are still carrying that one. I never heard of 'jlha', i.e. the one you are using.
This archive contains just a single executable, not a disk image btw. - as is to be expected with lha archives containing Amiga stuff.
Because ADF is a terrible, horrible file format that needs to go DIAF.
Thank god you're en expert on everything, not just Google and diskmags.