Does A Record sub domain mapping hurt seo for client

Hi,

I am running an advertising Landing page from a sub folder multisite installation, domain mapped to a subdomain for a client..

So, specifically here http://www.corriedmarketing.co.uk/marketingsuite/ is where the multisite is installed, and one of the sites there is http://www.corriedmarketing.co.uk/marketingsuite/idealwindows

which we have domain mapped to http://offers.idealwindowsandconservatories.co.uk using an A record to point to the ip, and the landing page url is then offers.idealwindowsandconservatories.co.uk/marketingsuite/ because this is a sub directory install on /marketingsuite..

Convoluted I know..

The question is;

Is there any impact on SEO for the client's site idealwindowsandconservatories.co.uk - as their current web guys claim.

I can't see how myself, but thought I would get your input.

The landing page has unique content and has individual menu links over to sections of their main site - providing backlinks to it, so there is no duplicate content etc.

I'd appreciate input on this, for this client and for future reference in applying domain mapping,

thanks,

Iain