Interpretting WS2812 datasheet data input requirements
That is an "or". \$V_I\$ is supposed to be a digital input, so the valid states are either 0 (\$V_{SS}\$) or 1 (\$V_{DD}\$), and the input current value is valid for both in steady state (the input is supposed to have an impedance of at least \$5\ \mathrm{M\Omega}\$. It's most likely connected to the gate of a FET, so there is your high impedance.

Pulling up the GPIO on the RasPi is a problem. The GPIOs are not designed to see higher voltages than the processor supply voltage, which is \$3.3\ \mathrm{V}\$.

Instead, I'd just connect the WS2812 directly, through a small (\$33\ \mathrm{\Omega}\$) series resistor if you have one. The voltage drop across the resistor is negligible at \$1\ \mathrm{\mu A}\$, but it protects the Pi if the first WS2812 fails and shorts D to ground.

This is also out of spec (\$3.3\ \mathrm{V} &lt; 5\ \mathrm{V}\centerdot0.7\$), but usually works.