Wow: This is a very unusual request, and I'm not sure if it is possible.
I can only think of a single (very remote) possibility: Give access to the root of the repository to this group of people, but deny them access to the branches, tags, and trunk subdirectory themselves. It is possible that the user might be able to do a svn log on the root of the repository, but won't be able to checkout the files themselves.
I really don't have time to setup a complete test, but that's the only possibility I can think of. Something like this in authorization. I'm not even sure if this syntax would be 100% correct:
[groups]
dev = tom, dick, harry
other = bob, carol, ted, alice
[myrepos: /]
@dev = rw
@other = rw
[myrepos: /trunk]
@dev = rw
@other =
Another possibility: Use a web based program or a client server type program to view the log information. For example, imagine a limited program that can do either "svn ls" or "svn log", but that's all. The server could have full access to the Subversion repository, but only allow for limited querying.
The final possibility (and my preference) is to use a continuous build system like Jenkins to do a build on every check in. Jenkins will make it easy to see what changed in each build, and will even list the files that were change, but deny access to the source. It is very likely that this is good enough for this particular group of users.
Even better, Jenkins can integrate with Redmine, so Redmine can pull in the changes.