Yes. As a DM I use roaming groups (Goth Raiders, for example), territorial groups (local bands or warbands, petty warlords), criminal groups (such as the Khomainahas, or other smugglers, gangs, organized criminals, pirates, etc), invaders (Huns, Vikings, Persians, Bulgarians), mercenary groups (bands of let's say Vikings or Rus in pay of the Empire), competing groups (such as the Hoshi), secret or occultic groups (such as the Heires or Glyphers), and groups of Nemeses (such as the
Consociatio).
Now as to whether the party actually encounters these groups, that depends heavily on where they are operating, how the opposition is operating, and what the general conditions may be at the moment.
(Such as, "is the party in a good place to be ambushed by brigands," "are the Goths currently raiding," "are the Huns on the warpath," "has the party accidentally stumbled upon the hideout of a group of smugglers," or "has the Consociatio accidentally discovered the party while the party is unprepared?")
To me the world, and the setting we use is a very dangerous place.
It always remains an open question as to whether the party will by fate or fortune happen upon a potentially dangerous enemy. But an adventuring world is usually a very dangerous place by very nature, and the odds of encounters with potentially lethal enemies is always a strong possibility.
In my opinion the party should always be prepared to be attacked or ambushed, the DM should always be ready with a suitable and prepared enemy, and the players should always be prepared to ambush their many enemies and opposition, should the opportunity present itself, or the conditions make such an encounter necessary at the moment.
To me if you're not ready for the dangers of an adventuring and dangerous lifestyle (which in game terms means you could be attacked, or should be ready to attack at any given moment) then chances are you should be probably be in another line of work, or you should expect to have a foreshortened lifespan.
Preparation for danger is always preferable to being endangered by lack of preparation.
I think surprise attacks and ambushes teach an individual that the very best lesson regarding real danger is to assume you're never really out of it.