Short answer: Probably okay if you have only a few of them, but you will probably see degradation if you have lots of them in a cluster.
Longer answer: The Shannon–Hartley theorem tells us how much data can be pumped though a communications channel before we get unrecoverable errors. The data capacity for modulating the backscatter will come out of the same "bucket" as the capacity for the active transmitter, meaning it will slightly reduce the channel capacity available to the active transmitter. In practice, the active transmitter is probably not near to the theoretical limit and has a rate much greater than the backscatter transmitter, so it can easily correct the errors caused by the backscatter modulation. Increase the amount of data on the backscatter channel, by upping the rate or number of transmitters, and the active transmitter probably won't be able to recover from the loss of available capacity, and the user will see an increase in bit error rate.
I'd like to see a MIMO version of the backscatter transmitter!
Longer answer: The Shannon–Hartley theorem tells us how much data can be pumped though a communications channel before we get unrecoverable errors. The data capacity for modulating the backscatter will come out of the same "bucket" as the capacity for the active transmitter, meaning it will slightly reduce the channel capacity available to the active transmitter. In practice, the active transmitter is probably not near to the theoretical limit and has a rate much greater than the backscatter transmitter, so it can easily correct the errors caused by the backscatter modulation. Increase the amount of data on the backscatter channel, by upping the rate or number of transmitters, and the active transmitter probably won't be able to recover from the loss of available capacity, and the user will see an increase in bit error rate.
I'd like to see a MIMO version of the backscatter transmitter!