It kind of depends.
If the forum is licensed under GPL there can be some complications because SMF's license isn't GPL compatible. The reason the Joomla! bridge isn't distributed anymore is because of that little issue (basically, the Joomla! team decided to do a Stallman-esque balls-to-the-wall word-for-word interpretation of the GPL*). Licensing issues, most bridges still seem to be geared toward phpBB2 for some reason.
SMF is well-supported by some bridges, though. The Mambo bridge is still well supported. In addition, there are a couple of portals available that are based around SMF, namely mkPortal (which s.net v2.0 used) and bloc's popular tinyPortal. Those have enough features to work well for community-oriented sites and, since they're built from the ground up to use the same database, there aren't any integration issues.
I only have personal experience with the now-defunct Joomla! bridge so I'm not completely sure what the state of fully-blown CMS's is. Based on what I've seen in the bridges section on the official SMF forums, it seems like support for it has definitely been on the uptake.
*<soapbox>This is why the GPL isn't taken seriously in the commercial world. It's written in such a way that, if followed point by point, it's pretty much incompatible with anything other than other completely open licenses. If there's even the vaguest limitation in another license (even if it could be still undeniably be considered open or shared source) to the point that the GPL and it aren't compatible it's illegal to link the programs. People need to start using the LGPL more.</soapbox>
