Importing Levels Into Hammer
What's supported
Hammer has built in support for more than just its native .vmf file format. It can also open .rmf and .map, not suprising as they were teh precussors to the current .vmf and have many similarities. All thats needed is to change the file type being browsed for by the open file dialog. A key factor to note is that while all the information may get loaded a lot of entity information will not mean much without a proper .fgd.
Importing Unsupported Types
At its simplest you can't, wheter the level exsisted for UT or wheter it was made in AutoCad unless the file format matches up to whats mentioned above it's not getting into Hammer. Applying coverters to it in order to make the data conform to the right format is the only way; however, you'll be lucky to find one. Level design is meant to be done in a level deisng program, and to top it off level designment programs don't cross apply between games easily. Expecting to get a level design from another program into is wishfull thinking that may cause a lot of issues. The core part of the argument is listed below.
Pros
- Possibly more familiar with program speeding up early stages of development
- Some design suites may allow creation of obscure geometric forms more readily
Cons
- Invalid Brushes much more likely
- Likleyhood of skewed, or misaligned textures causing Vrad compiling issues
- No access to all textures
- File conversion once finished with a program
- Inability to create/modify entities
- Testing becomes a long and ardous process in order to fix the design before conversion
- Poor alignment (grid locations being integer powers of 2)
- Inability to place/align models
- Displacement terrain functions not avalible
- No way to paint alpha
- Complicated back and forth debuging process
- Hammer neccesary for essential level components so multiple development tools in use
Summary
If the level's file type is supported go ahead and import it in to Hammer and use that base. If its not, its probably not worth the effort to change the file format and then to alter the information so it doesn't cause issues. Not to mention then adding in the data the other programs couldn't create would take longer and require more effort than redesiging from scratch in Hammer would of anyway. Its possible, but its not advised. Hammer is not a difficult tool to learn and most of its limitations are due to technological limits of the objects being created.