There are no configuration option to define per-workspace behaviour on the bar.
But there is the bar mode
command which allows changing the display mode of the bar(s) during runtime. Also, the i3 IPC has events for workspace changes, so you could change visbility of the bar every time you enter or leave the workspace in question.
Here is a simple prototype using i3-py:
#!/usr/bin/env python
import i3
def wsch(e, d, s):
if e['change'] == 'focus' and e['current']['name'] == 'special ws':
i3.bar('mode', 'invisible')
else:
i3.bar('mode', 'dock')
s = i3.Subscription(wsch, 'workspace')
This will make the bar invisible every time you go to special ws and make it docked if you go anywhere else.