1) No. Well, potentially as a crypto accelerator, but QAT and Chelsio T6 are less power hungry and more available. GPUs are so expensive/unavailable now that leveraging them in creative ways makes less sense than just using a NIC like the CX6-Dx, which has crypto as a low cost feature.
2) These are just static files, all encoding is done before it hits the CDN.
I wonder if one creative (and probably stupid) way to leverage GPUs might be just as an additional RAM buffer to get more RAM bandwidth.
Rather than DMA from storage to system RAM, and then from system RAM to the NIC, you could conceivably DMA to GPU RAM and then to the NIC for a subset of sends. Not all of the sends, cause of PCIe bandwidth limits. OTOH, DDR5 is coming soon and is supposed to bring double the bandwidth and double the fun.
2) These are just static files, all encoding is done before it hits the CDN.