The correct command to generate alerts for an event when the temperature of the database servers in an Exadata Full Rack exceeds 30C is "dbmcli -e "create threshold ds_temp comparison='>', critical=30" on each database server". The dbmcli is the command-line interface for the Oracle Database Management Agent (DMA), which allows you to perform various management tasks on the Exadata servers. This command creates a threshold for the ds_temp metric with a comparison operator of ">" (greater than), and a critical value of 30. The threshold is set on all database servers in the Exadata Full Rack, so when the server temperature exceeds 30C, an alert will be generated.

In an Automatic Storage Management (ASM) environment, failure groups are used to provide redundancy for the storage disks. Failure groups are used to group together a set of disks and ensure that no two copies of the same data are stored on the same physical disk or storage server. This way, if a disk or storage server fails, the data can still be accessed from the other copy.
For example, if the disks in a failure group are mirrored, one copy of the data is stored on one set of disks, and the other copy is stored on another set of disks. This way, if a disk or storage server fails, the data can still be accessed from the other copy.
ASM failure groups also provide the option to spread the data across different storage servers, this way, even if a storage server fails, data can still be accessed from the other storage servers in the group. This will improve the availability of the data.

According to Oracle's documentation1, the customer options for hosting the Platinum Services Advanced Support Gateway are:
Provide individual x86 64-Bit gateway hardware1
Purchase the recommended x86 64-Bit gateway hardware from Oracle1
Install on Oracle Database Appliance2