冨 is a common variation of 富.
冨 - Wiktionary
Also, 富(or 冨)士の山 is really used to refer to 富士山, as in the wikipedia page you found.
As for 山, it's often the case in calligraphy that the brush is stopped after a line and then writes the next stroke even if it's usually written in one stroke by pen or pencil. This is applied even to the first touch of a stroke, and as a result, it seems like a dot and connected or slightly separated line, not a simple single line, as you can see in the vertical line or the upper horizontal line in 士. This technique is called とめ. There is no problem to seem to be written in different stroke counts in calligraphy.
Thus, that's a very common calligraphy for Mt. Fuji.