First things first:
Each Informatica domain has at least one gateway node, even a single-node installation (then the only node is "the" gateway node). Worker nodes can solely be included in multi-node domains.
As far as I know (honestly I haven't followed the development of TDM over the past two years, so I may be wrong here), TDM is meant to be installed and run in a single-node domain. That does not mean it cannot be installed on a server grid, but it usually makes limited sense to do so.
Technically a PowerCenter repository service always runs on one node, either on its "primary" node or (if that node fails to work) on one of its "secondary" nodes.
Things are diferent for an Integration Service because these may be defined to run on either a single node or a server grid (which may consist of one or more nodes in the domain, not all nodes must participate in a grid). For TDM I don't know whether an Integration Service on a server grid would run smoothly, that's something I have not tried yet.
To be 100% sure that your TDM environment runs fine, I would set up an Integration Service to run on one single node (no matter which one) for TDM.
If no one e.g. from Informatica can confirm that TDM is supported to run on a server grid, I would not even try it; chances are small but greater than zero that you may "kill" your installation if anything goes wrong (or, even worse, get intermittent errors and sometimes wrong data).
Thanks for your reply. I believe you are correct that TDM is meant to be run on a single node domain. Aside from TDM, a general question about multi-node domains and grids: is a multi-node domain a grid by default? Or is a grid a specific "type" of multi-node domain? In other words, if I have multiple nodes in a domain is that always a grid? Just trying to understand terminology.
To be honest I am not 100% sure; Informatica does change its terminology from time to time, so my information might well be outdated by now.
As far as I understand it, a multi-node domain is indeed a "server grid". However, in order to distribute PowerCenter workflows (or even sessions) over more than one node, you need the "PowerCenter Server Grid" option in your license; without this license option you can set up as many Integration Services as you want, but they can only run on one single node.
Again, this might be outdated by now. Can someone more knowledgeable than me please confirm or correct me?