>>> Can I assume or imply that the C=O in an ester
linkage to be taken as a carbonyl group as well? <<<
Yes, of course it's a carbonyl group (defined simply as C=O);
but that does not necessarily mean a carbonyl group in an
ester will always behave identical to carbonyl groups in
aldehydes and ketones - it certainly doesn't.
>>> That is to say, can C=O in ester undergo reactions
similar to ketones? <<<
Only to a limited extent, in some reactions only.
>>> If I have CH3COOCH2CH3, can I use the
tri-iodomethane test to distinguish it from, say CH3OOCCH2CH3?
<<<
No, the iodoform test will not work for methyl esters, methyl
carboxylic acids, methyl amides, etc. It only works (ie. gives
positive result) with methyl aldehydes, methyl ketones, and methyl
secondary alcohols (that can be oxidized to methyl ketones).
To distinguish both compounds you stated above, carry out
hydrolysis, then oxidation. CO2 gas will only be produced for
the (reaction pathway products from the) parent compound
CH3COOCH2CH3, but not for CH3OCOCH2CH3.