nope they dont...they create separate sql databases and can be operated...havent tried opening them simultaneously though while playing...that will possibly interfere...
Both PT4 and HEM can work on the same computer using the same PostgreSQL server, but the two applications use different databases. Please use versions 8.4.x or 9.0.x to assure PostgreSQL compatibility.
Yes, you can use both at the same time. The only thing we suggest to people doing this is to disable the archiving of imported/processed hands in one of the applications so they aren't fighting over the files that need to be archived.