@Shentheman, thanks for asking. Documentation is certainly lacking. Unfortunately, I'm not familiar with using Robotiq with Gazebo, so I can't answer your question. Hopefully another user will be able to answer this.

The messages have the same content and thus the same md5 hash. You should be able to use them interchangeably.
I definitely agree that this collection of packages requites some TLC and happy to put some time in if we can then move it towards being released on the build farm/as debians - e.g. unify the S-Model messages for control and articulated as robotiq_s_model_msgs and release them (they are e.g. required on clients that do not require the drivers and the whole meta package to be built).

$ rosmsg md5 robotiq_s_model_articulated_msgs/SModelRobotInput
4d0701156e580a420c48833f57bc83f3
$ rosmsg md5 robotiq_s_model_control/SModel_robot_input
4d0701156e580a420c48833f57bc83f3

@wxmerkt, thanks for helping answer. I totally agree with the improvements that you suggest. The lack of progress is due to a lack of time on my part. I'm happy to accept PRs submitted by the community.

On another note, I just noticed that the folks at Clearpath noticed that a field in the SModelOutput was missing and added it (incompatible with this repository/upstream):

https://github.com/DualUR5Husky/robotiq/commit/73e5219cfab7d9d19f3c1a6b76548c1288ff9b76

I just encountered the same issue and mixed up the robotiq_3f_gripper_articulated_msgs and robotiq_3f_gripper_control.
While the "input" messages have indeed the same hash, the "output" messages differ:

$ rosmsg md5 robotiq_3f_gripper_articulated_msgs/Robotiq3FGripperRobotOutput 
d0c643ca7dd9fdb2d935922bf6659387
$ rosmsg md5 robotiq_3f_gripper_control/Robotiq3FGripper_robot_output
31ba91390a569c669af204c3d006a806

since the rGLV is missing in robotiq_3f_gripper_articulated_msgs as @wxmerkt pointed out.

I think it would make sense to go for a single set of messages for the very same purpose. I don't see the point in having twice the same messages. I am in favour of using the robotiq_3f_gripper_articulated_msgs since they already contain documentation about message content.

Would you accept a PR that replaces the robotiq_3f_gripper_control messages by robotiq_3f_gripper_articulated_msgs (including rGLV)?