I don't have any firsthand info about that herd, but you can find success info under the "Statistics" link under "Big Game" (http://wildlife.state.co.us/Hunting/BigGame/Statistics/). 

The herd numbers can be fund under Herd Management.  I think you would want to read about E-30 and E-31 DAU (http://wildlife.state.co.us/Hunting/BigGame/HerdManagementDAUPlans/)

Also, you might want to check out the Big Game Hunting Guide for the Southwest Region (http://wildlife.state.co.us/Hunting/BigGame/HuntingGuide/). 

Finally, yes, the OTC tags are truly "over the counter."  You can go anywhere CO hunting licenses are sold and pick one up and hunt any of the areas highlighted on the map you already found. 

Over the past 20 years I've hunted Unit 74 about 16 seasons.

The Hermosa herd is listed at 4500.  That is the dominant herd in the unit.

The success rate in 74 fluctuates from about 18% to about 25%.  I guess I could describe it best by saying that you probably won't bag an elk there unless you know what you are doing.  It is an attractive area because there are tags available.  The terrain there is such that the elk really don't need to come near roads or trails so you usually need to hike pretty far in to have a chance.

I highly doubt that trophy hunters are deflating the success rates.  Those are pretty normal numbers for all of Colorado.  Success has more to do with access to game in my opinion than density (the top elk density unit the state has poor success rates).  Wilderness areas, roads, terrain, vegetative cover and other things have an effect, and 74 is pretty normal for a mountainous unit.

11 is a productive unit, but it's not really a mountainous unit and not exactly what most nonresidents picture when they want to come out to Colorado.  Decent access and high success there though.