The Merge Agent failed because the schema of the article at the Publisher does not match the schema of the article at the Subscriber. When syncing a SQL Server 2008 subscriber with a publisher, the sync fails at around 98% with this error message:


  The Merge Agent failed because the schema of the article at the Publisher does not match the schema of the article at the Subscriber. This can occur when there are pending DDL changes waiting to be applied at the Subscriber. Restart the Merge Agent to apply the DDL changes and synchronize the subscription.


We have 30+ subscribers -- all of which are working except this one.

Is there any harm to other subscribers to restart the agent?

Bonus Points:

b) Is restarting the agent a good solution, or should I be looking elsewhere when I see this message?

This error message is also featured in Issue with SQL Server 2008 replication
I have run into this in the past.  In my experience typically this will resolve it's self by just restaring the sync process.  From the client in a pull situation, or restart from the publisher in a push situation.  

In short the application of DDL changes ran into a conflict but restarting the sync will usually resolve the issue.  And no, it doesn't start from the beginning, it should just pick up from the point of failure.

It also wouldn't hurt to make sure that your snapshot is up to date and current.