You can always *apply* for PR but unless you meet the requirements it will be refused. A 457 visa does not guarantee PR.
If one person is granted PR, it get granted to the spouse as well.
I can't comment on what you were told on another forum, but here is a list of the problems and issues that many people have encountered on a 457 visa:
Employer sponsored migration visas are given priority. Download and read booklet 5 to find out about sponsorship for permanent employer visas.
The company might not be aware that since the rules changed in April 2005, sponsoring for ENS is much simpler provided your partner can get a skill buttessment. The employer does not normally have to prove they cannot recruit an Australian.
Booklet 6 will tell you about most general send visa options.
You should think about the options facing you, and work from there.
The United Kingdom allows dual citizenship. So does Australia.
However, if you ever want to apply for Australian citizenship (you'll need to live in Australia for a few years as a PR), you will need to get the permission of the German government in advance (otherwise German citizenship will be lost). info.org-relaunch-info-consularservices-citizenship-einbuergerung.html
-- This is not intended to be legal or professional advice in any jurisdiction
