Just to clarify the terminology of the different visas:
1)
Spousal visa: 27-month visa allowing you to move to the UK to live with your spouse. You must live in the UK for 2 years before you can apply for ILR.
2)
Spousal visa with KOL Req'd: 27-month visa allowing you to move to the UK to live with your spouse, but as you have been married for 4+ years, you can apply for ILR as soon as you have taken the KOL test. This will only be granted if you request it specifically and include your marriage certificate and last 4 years of tax returns (to show you have been living together).
3)
ILE: Permanent residence issued
outside the UK for those who have been married 4+ years AND have already taken the KOL test.
4)
ILR: permanent residence issued
inside the UK for those who are already living in the UK on a spousal visa or a spousal visa with KOL Req'd and have taken the KOL test.
So, as you can see, you will be applying for a spousal visa in the US (and requesting a KOL Req'd stamp), because you cannot apply for ILE or ILR until
after you have taken the KOL test, and you can't apply for ILR unless you are already living in the UK.
He enters the UK on that visa and is immediately eligible to sit the KOL Test (foregoing the 27 month probationary period) and following payment (and of course a pass)will be given ILR?
Well, he won't just be 'given' ILR when he passes the test. After he has taken the test, he will need to go through the visa application process for ILR... filling out the application form, gathering the required supporting documents, having biometrics taken again, sending off the documents to UKBA (or applying in person and giving biometrics on the day, although it costs more to do this) etc.