RG
the short answer is no.
they offer you a spread which allows them to lay off in the market at a profit.
they could not (in general) give a damn what system people use.
but heavy stakes which continually win, may present difficulties for them.
so they will give you a personal quote for that sort of money/client.
for example Cantor have done a special deal with one client using cfd's to build up a huge stake in a company, so obviating the declaration rules. And he gets the voting rights.
I should add that its currently being investigated by FSA and
somebody is going to get their wrist slapped rather smartly.