Yes, the Wally is designed to be a straight plug-and-play replacement for a ViP211k on a DPP LNB or switch. Even with an older DP LNB or switch, there is a code that Dish can place on your account to disable the second satellite tuner on the Wally, which would make it compatible. In that case, the model listed on the Diagnostics screen would change to Wally T.
Having the OTA dongle and EHD both connected to the Wally works very well. I have tried this with the really old single-tuner dongle and multiple models of dual-tuner dongles (although only one OTA dongle at a time, obviously) and have not had any issues related to that. By adding a simple USB hub, you can even have more than two USB devices connected to the Wally at the same time. It is recommended to plug the external hard drive directly into one of the Wally's USB ports, and plug the hub into the other USB port. The hub would allow you to have the OTA dongle, Wi-Fi adapter, and Bluetooth adapter all plugged into the Wally at the same time. I have never used the Bluetooth on a Wally, but I have had the OTA, Wi-Fi, and EHD all hooked up at the same time without any issues. At least one other member here has reported having all four USB devices connected to a Wally at the same time, and that also worked well for him.
The minimum EHD size for a Wally is 500GB, which is larger than the minimum needed for other ViP or Hopper receivers. The maximum EHD size supported by a Wally is 4TB.
If you are interested in a spare ViP211k just in case, I recently offered mine to another member here, but never heard back from that person. So, I will make the same offer to you, if you would rather keep using ViP211k instead of switching to a Wally.