Recently tracked down the issue with why satnogs-client and activating the bias-T on the RTL-SDR blog v3 receiver works-but-doesn’t.
The current version of GNU Radio that the Ansible scripts install is exactly 0.0.1 point revision older than required to support the bias-T. This is because it depends on a version of gr-osmosdr just before support was added for the feature, which in turn depends on a slightly-too-old version of librtlsdr that exposes the API / ABI for controlling the GPIO pins (which enables the bias-T LDO regulator).
Adding bias=1 to SATNOGS_DEV_ARGS is indeed the correct way to activate the bias-T on that receiver, except that the version is slightly too old wherein the option is ignored. Worse receive performance is then simply because the LNA is not powered at all and attenuating the signal instead 
Pretty much any upgrade to satnogs-client-ansible that bumps the GNU Radio dependency will also cause the bias-T option to work as advertised. Moving the Raspberry Pi image to buster is sufficient for this to happen – a task that is being worked on already most likely. Enabling bias-T use without additional hardware is an important enabler for lowering the expertise required to setup a decent-performance GS.
This issue is why none of our stations (yet) have LNAs
https://network.satnogs.org/stations/834/
https://network.satnogs.org/stations/841/
https://network.satnogs.org/stations/890/
The short term fix is to re-compile the dependency chain of gnuradio <-- gr-osmosdr <-- librtlsdr. I ran out of steam and time before writing down the specific version numbers required for this that are still compatible with the released version of gr-satnogs and plays well with satnogs-client-ansible. If/when I do this, how-to details will get posted in the forums.