Short Answer
As DigitalNinja pointed out, an Android phone will always support Central role functionality by default, so if your phone supports BLE, then it can definitely operate in the central Role
Long Answer
You're right, the API might not be straight-forward but this is down to how Bluetooth Low Energy (BLE) API was added to Android and even down to the history of BLE technology itself.
When BLE was first introduced, it was aimed to be for sensors only (e.g. thermometer, heart rate, proximity, etc) and devices that talk to these sensors. The sensors were the peripherals in this case, and the devices that talk to these sensors are the centrals. The peripherals were the true Low Energy (LE) devices, as they would just advertise and send data once in a while. Centrals on the other hand would not be very power efficient as they would have to continuously scan for devices, connect to these devices, and remain in charge of maintaining and monitoring that connection, meaning the radio would be on for a much longer time when compared to the peripheral.
When Bluetooth Low Energy (BLE) API was added to Android, it supported Central role only. In other words, you could write an Android app to scan and connect to peripherals (sensors), but the Android device itself could not act as a peripheral (Because the assumption was that you wouldn't need an Android device to act as a sensor). This was done in Android 4.3 (API 18).
As people started to use BLE more often and the technology matured, it started being used for all sorts of different applications (e.g. virtual serial port, data transfer, beacons, etc). Moreover, standalone central devices started appearing in the market and there was a need to use them with phones or at least test them out against phones/tablets during the development stages. As such, the distinction between central and peripheral started becoming fuzzier and fuzzier, and there was a demand for Android to start supporting peripheral role. This is when the BLE API was updated to introduce peripheral role functionality, which happened in Android 5.0 (API 21).
So to answer your question, if BLE is supported on an Android device then it is safe to state that it will by default support central role as this is the foundation of the BLE functionality for Android. However, API was introduced later to support the peripheral role, which is why not all Android devices that support BLE will support peripheral role.
Finally, please note that isMultipleAdvertisementSupported is a different feature which indicates if your device supports sending out multiple adverts at the same time. Some devices support sending out different adverts simultaneously, while others don't. However, this does not mean that they do not support advertising at all. A device that supports isMultipleAdvertisementSupported will definitely support BluetoothLeAdvertiser, but the other way around is not guaranteed.
To conclude, the safest way to check if your device supports central and/or peripheral role is through the Android version and the API level used, as indicated by the two links above. On Android 5 (API 21) onwards, you can write applications that support both central and peripheral roles, whereas before that you can only write applications for the central role.
I hope this helps.
