my understanding (and i'm not an expert - just trying to help with the discussion) is that getting sufficient entropy is quite hard. i vaguely remember at least one issue, perhaps on startup, where there was insufficient entropy to do something, and so people switched to some other less random source and screwed everything.
so if this reports unlimited (or at least, larger than anything else) entropy then there are likely situations where it's the only source available (people don't typically have lava lamps wired up). and then an attack seems possible.
[edit: while startup is the case of the bug i remember, you might "consume" entropy faster than it is generated at other times too (i imagine a server running https has a fairly high demand for entropy, for example).]
i'm sorry, this is just incoherent to me. i have no idea what you're trying to say, or how it fits with my comment.
i was trying to explain why an untrusted hardware rng cannot be improved in some cases (because of limited entropy from elsewhere). and i don't see how what you are saying addresses that.
(1) Chaining rnd generators is fine as long as they are not correlated somehow. If there is any correlaton, the output may be weaker. (Consider chainig two exactly same generator as a corner case.)
(2) In this case we don't chain generators; you would loose the speed of the integrated one otherwise.
