can I drive 100 or so LRAs with WS2811 controlling DRV2603?
Not sure if you have found answers to all your questions. You could connect the DRV2603 to a Lithium battery supply. You need to maintain the voltage rating of the datasheet (2.5-5V) rather than connecting to a current source.

When the LRAs are vibrating you will see the DRV2603 will consume around 30-90mA to vibrate the LRA.

For vibrating multiple LRAs, you can hookup say OUT+ of 10LRAs to 10 DRV2603s and connect the rest of OUT-'es to a switch. There is an example of this one in the EVM schematic. I would get a digital switch for that one so that you can communicate with a micro-controller.

You can also post your question on the E2E TI Haptics forum too for an in-depth Haptic questions.