I was on an engineering foundation year 3 years ago, having not studied maths, physics etc for 8 years! Granted, at GCSE level I got A* in both, and then worked a technical job for 5 years, however, I was rusty to say the least! And, I didn't have those subjects at A level.
Our foundation maths teacher was AMAZING! We started on week one with decimal places would you believe, and ended on integration and various other A-level stuff. Physics/mechanics was similar. With a foundation year, they give you exactly what you need for the degree, and so can even put you at an advantage to those who come in with A levels when you eventually progress to your first year of the actual degree. What I mean by this is, you don't just do maths and physics topics (at least we didn't). We did a "skills" module as well, containing report writing, presentations, use of Excel (which is a great modelling tool). In fact, myself and my mate are arguably the best students on my course.....both of us ex-foundation guys!
In terms of the level of maths involved, as whizz-kid said, engineering principles span across all disciplines, hence the maths is also pretty similar. At my uni, the mechs, motorsport, and I believe aero guys all sat the same maths modules.
With regards to employers views on a foundation year.......they will not care! You will need to have good marks at Masters level if you are serious about progressing in the engineering field. At this point, nobody will give a damn what happened prior to university study! My A level grades are wack........A/D/D in random subjects. Why? Because I was a stupid 16 year old when I chose them! At 27, I can assure you I am nothing like that person now, and employers will know this. Just plough all your effort into your higher education study and you'll be fine!
Ace