Can the Jaguar push a higher horizontal resolution? Does it use graphics hardware similar to the Atari ST family?

Completely different. The ST and TT used bitplanes whereas the Jag is chunky, and can support both YUV and RGB colourspaces. 640x200 is possible at least https://youtu.be/XI3Pvx5Yh1U?si=2bp93CeNYPTGZZic