On the question validation of licences, my understanding is that a validation can only cover privileges of the licence being validated. Therefore, if you need a type rating then it has to be added to the licence in accordance with the laws of the state which issued the licence.
Yes you do need ATPL knowledge to obtain a type rating. Annex 1 to the Chicago Convention and JAR-FCL are in agreement on this:
Annex 1
2.1.5.2 Type rating as required by 2.1.3.2 a)
The applicant shall have:
c) demonstrated, at the airline transport pilot licence level, an extent of knowledge determined by the Licensing Authority on the basis of the requirements specified in 2.5.1.2 or 2.9.1.2, as applicable.
JAR–FCL 1.250 Type rating, multi-pilot –Conditions
(a) Pre-requisite conditions for training: An applicant for the first type rating for a multi- pilot aeroplane type shall:
(4) have met the requirements of JAR–FCL 1.285.
JAR–FCL 1.285 Theoretical knowledge
(See AMC FCL 1.285)
(a) Course. An applicant for an ATPL(A) shall have received theoretical knowledge instruction on an approved course at an approved flying training organisation (FTO). An applicant who has not received the theoretical knowledge instruction during an integrated course of training shall take the course set out in Appendix 1 to JAR–FCL 1.285.
(b) Examination. An applicant for an ATPL(A) shall have demonstrated a level of knowledge appropriate to the privileges granted to the holder of an ATPL(A) and in accordance with the requirements in JAR–FCL 1 (Aeroplane) Subpart J.
A CPL can act as co-pilot. Again Annex 1 and JAR-FCL are in agreement on this. Obviously the CPL must have passed the ATPL knowledge to have obtained the type rating necessary to act as co-pilot.
Annex 1
2.4.2 Privileges of the holder of the licence and the conditions to be observed in exercising such privileges
2.4.2.1 Subject to compliance with the requirements specified in 1.2.5, 1.2.6, 1.2.9 and 2.1, the privileges of the holder of a commercial pilot licence — aeroplane shall be:
d) to act as co-pilot in commercial air transportation in aeroplanes required to be operated with a co-pilot.
JAR–FCL 1.150 Privileges and conditions
(a) Privileges. Subject to any other conditions specified in JARs, the privileges of the holder of a CPL(A) are to:
(4) act as co-pilot in commercial air transportation.