Here is a conceptual thing to have in mind:
In the system there must be a component that do the stellar tracking, instruct the mount motor controller to rotate the mount following the stars. In the case of SkyWatcher system this component (surprisingly enough) is the hand controller itself. You can trade that hand controller to a software called SynScanApp runing on an Adroid/Ios device or a windows PC, but it plays the same role.
The mount itself is pretty dumb, just can rotate the motors at a given pace. That is why it is called a Motor Controller.
The hand controller/SynScanApp has a pretty high level interface, a computer can instruct the hand controller to slew to a given coordinate on the sky, and continue tracking from there, and can repeatedly report the position of the scope. All the tracking done autonomously by the hand controller or SynScanApp. That is why you need to do the initial alignment on the hand controller/synscan, and you cannot get rid of it later.
If you add INDI to the system there is two solution:
1. Use the hand controller/SynScan to do the tracking and connect INDI to it's high level interface. That is what indi_synscan_telescope driver do.
2. Let INDI do the hard work of all tracking and alignment process, and connect it to the low level interface of the motor controller. For that you need a totally different driver. In case of EQ mounts it is the indi_eqmod driver, in case of AltAz mounts there are two drivers: indi_skywatcherAltAzMount and indi_skywatcherAltAzSimple driver. For these you do not need a hand controller neither SynScanApp running anywhere. You can directly connect to your WiFi dongle connected to the mount or through a direct serial cable.
I try to do the same as you do, using a 10" Dobsonian mount with INDI. I've tried both method and I have problems with all of them.
For the direct method you can find my trials in this thread:
indilib.org/forum/ekos/6468-indi-skywatc...-wrong-position.html
I had connection problems and inverted coordinates, some solved some still waiting for relolution.
The synscan driver mostly works, here is the thread with my problems:
indilib.org/forum/mounts/6444-az-synscan...-explain-please.html
It is about the goto not working as expected. Lately I'm trying to resolve this, it seems to be due to using the "sync" function in KStars causes the hand controller having different picture of the sky in Alt/Az and RA/Dec coordinates. The thing is that when you give a sync to a star the indi_synscan driver works in a way that it sends the command to the hand controller which has the same effect as the PAE (Pointing Accuracy Enhancement) function does natively on the hand controller, effectively offsetting the coordinates in the vicinity of the given star.
I'm in an experiment modifying the indi_synscan driver to send the goto command to the hand controller in RA/Dec coordinates instead of Alt/Az coordinates, this way at least plate solving->sync seems to work and I had successes centering deep sky object in the field of view.
Also please note that for serial connection there are two different thing, one is connecting the hand controller and the other is connecting the motor driver. Both has an RJ11 type connector, but be careful, the two thing is totally different. Not just the pinout is different, but the voltage leves are different!
The hand controller interface use standard RS232 voltage leves (+/-12V) and the provided RJ11->DB9 type serial cable can connect to a standard PC RS232 port or an RS232-USB converter.
The motor controller has TTL (+5V) level signals and to connect that directly to the Raspberry you need a different USB-serial cable commonly referred in astro forums as "EQMOD cable". I made one for myself from an FTDI232 cable. The pinout for both the hand controller and the motor controller connector can be found in the SkyWathser hand cotroller manual on the last page.