The quick answer to the cosplaying Yojimbo is yes, mostly. The rules regarding it are as follows:
1) Under most circumstances weaponry or prop weaponry can't be worn with a costume while doing the Yojimbo work as you do not wish to frighten or intimidate any attendees you need to talk with. They should be left in the room until your time off. Exceptions to this can be made depending on the prop, and permission from the Yojimbo Manager
2) During hours working as a Yojimbo, you should not wear a mask as you want to appear friendly to attendees and approachable.
3) Any form of costume can be worn while working as a Yojimbo so long as it falls within the normal convention policy guidelines but you must be willing to wear the red haori in such a way as to keep it visible from front and back at all times you are working.
None of these have seemed to be a problem over the years, at least I have never recieved any complaints regarding them. If you have any questions about a particular prop or costume you are welcome to PM me about it this month, or PM the Yojimbo Manager after this month, once the job has been assigned.