Many dojo simply have a shomen; some dojo have a kamiza.
Walking between an instructor and a kamiza is a huge faux-pas.
The pattern remains present in dojo that have a shomen that is explictly not a kamiza.
For a fuller explanation of the way space is organized in a traditional dojo and why this might be so, Dave Lowry's article What Puts The Tao in the Dojo
is a good start.
Actually, every dojo has a shomen, and every dojo has a kamiza. It just depends on whether those who use it recognize them.
Shomen 正面 is simply "front". Wherever is decided to be the "front" wall of the dojo, that's the shomen. Typically, it's the wall opposite or farthest from the entrance.
Kamiza 上座 is a term of Japanese etiquette, and simply indicates the place of honor in any particular arrangement. Living rooms, dining rooms, dojo, theaters, meeting rooms, cars, even elevators! Where it is depends on what is considered the shomen and where the entrance/exit of the room is. Sometimes it's in front of the shomen, sometimes it's to the side.
There is some confusion, I think, due to a similar word: shinza
神座. The confusion arises because the kanji 神 is also read "kami". If you don't know that the correct reading for 神座 is "shinza", and you've heard the word "kamiza", it can be easy to assume that "kamiza" is written 神座 and/or that "kamiza" has something to do with 神. But while the two "kami" are etymologically related (along with 守 meaning "lord, guardian", and 髪 meaning "crown, hair"), in modern Japanese the meaning and usage is quite distinct. "Kamiza" is not even listed as an alternative reading of 神座, and 神座 itself refers to the resting place of the kami in a Shinto shrine (a place off-limits to everyone except the keeper of the shrine), not to anything in your typical dojo (or living room, for that matter).
In the article, Mr. Lowry is confusing three things: tokonoma, kamidana, and kamiza.
The kamiza, simply being the seat of honor, is rather flexible and ephemeral. It is not, in fact, tangible.
The tokonoma is a slightly raised decorative step in front of the shomen, on which are placed flowers and over which often hang scrolls of calligraphy and pictures of Ueshiba Morihei/Kisshomaru/Shioda Gozo/Saito Morihiro, etc. This is often confused with kamidana, but is quite distinct. The kamiza in a dojo is almost always in front
of the tokonoma, if it has one, but the tokonoma is not itself the kamiza.
A kamidana is a raised shelf (much higher than the step of the tokonoma). It is a Shinto altar that contains offerings to the kami
(which in this case can mean both what we term "gods" in English, as well as what we call spirits). Often it will have a rope and paper lightning hanging across it. A famous kamidana in aikido is the one at the Iwama Dojo