Hi Borat,
A. Do I need to create a new Alert Object Type for EACH unique macro alerts? System (maintain alert types for database alerts in spro SCM Basis) is allowing me to create NEW alert object types arbitrarily
I don't think so, and not experienced as well. Since alert object type represents alert varients (database, dynamic etc.) of different application areas, and almost all the time you don't intend to work with whatever application areas are provided by SAP.
Seriously i didn't faced any situation where i need to create new Alert object type.
B. Do I need to create a new Alert Type for the UNIQUE Alert Object Type I defined above when Alert Type "Standard Status Alert" in combination with freely defined "Alert text" shown in the image above is doing the same job of generating a database alert Alert (functionally) ? The point is I do have an Alert Text that can be unique for each Alert.
In case you want to show only relevent alerts to your planners, you can go ahead and define custom alert types, in case that is not the case you can use standard status alert, custom alert types enables the demand planners to view only relevant DP alerts and also enables to setup a process for proper maintenance of Alerts on a periodic basis. This is particularly useful while setting up alert profiles and differentiating the alerts generated by other modules such as SNP. So based on the business requirement you can take appropriate action. 
C. In the Define database alert types for demand planning and SNP ugly looking screen in SPRO SCM Basis, I see two columns both with SAME labels viz. "Alert Type". The technical name of one of them is ATID and the other one is AT_ID. Which of this is Alert Object Type ? I can't seem to make out that either of that is Alert Object Type.
In fact there are three columns, middle one is alert object type both right and left ones are alert types.
Left and Right ones have same heading, but these nos. are not visible in both Macro alert step and Alert profile, what you see is the text which is assigned aginst each row.
Field AT_ID is the actual alert type, which is the field of table /SAPAPO/ATYPES (table stores all alert type information), other field ATID is the mapping field from table /SAPAPO/ATUID (table for storing Mapping information of Unique ATID for AOT + AT_ID), its a bit confusing the way it is designed, but this is the way it is.
Hope i am able to clarify you doubts, without confusing you any more.
Rgds
Sourabh