Yes. An ANSI keyboard can be used with an ISO keysetting, with some caveats.
I would assume that the key above the ANSI enter would map to the left of the ISO Enter, so you just need to learn to find the £$}-key in a different spot (above the ANSI Enter).
The <>\-key would be missing though, as ISO keyboard have an extra key compared to an ANSI keyboard, so you wouldn't be able to write <, > or \ without some custom keybinding/application.
EDIT: So to answer your question. Yes, one key would be missing, and one key would be moved.