On platformio/platform-raspberrypi, yes.
Though with Arduino-Pico (Earlephilhower) support, PicoProbe Debugging by maxgerhardt · Pull Request #36 · platformio/platform-raspberrypi · GitHub merged it will have two Arduino core options.
The PR, that enables Arduino-Pico, also enables you to access the Pi Pico SDK, like the documentation says.
Alternatively, as discussed in e.g. RP2040 not starting - How to set adjust the startup delay for crystal stability on custom designs - #2 by maxgerhardt, there exists GitHub - Wiz-IO/wizio-pico: Raspberry Pi Pico development platform for PlatformIO, which gives you access to only the Pico SDK (called framework = baremetal there).