At least in the QGIS 2 version, an "OSMtools" toolbar is created, but the plugin button is added to the standard "plugins" toolbar.
idk about best practices with qgis toolbars, but creating one toolbar for each plugin seems not optimal anyway, maybe consider the "web" or "plugins" toolbar?
At least in the QGIS 2 version, an "OSMtools" toolbar is created, but the plugin button is added to the standard "plugins" toolbar.![screenshot from 2018-03-14 11-07-53](https://user-images.githubusercontent.com/7880552/37396058-1de21ade-2778-11e8-8a23-3c92e59c46a6.png)
idk about best practices with qgis toolbars, but creating one toolbar for each plugin seems not optimal anyway, maybe consider the "web" or "plugins" toolbar?