To the OP, short answer - yes.
I moved from a large rock band - 3 guitars, drums, keys, multiple singers and me, to a jazz influenced combo of just a singer, a guitarist and me. The main takeaways have been:
1. You are now the timekeeper. The others will naturally look to you to keep everything on-track and together. This means that you will likely need to play a little more simply. Specifically, making sure the "one" is very much on time and pretty much always the root of the chord. You can sometimes do an inversion to keep things interesting, but again, the "one" needs to be there whatever note you play.
2. As the number of instruments decreases, there is good news and bad. The good news is that there is much more sonic space available to you. The bad news is that there is nowhere to hide or be buried in the mix. As such, my advice would be similar to point #1 - play cleanly and correctly, even if it means playing simpler lines.
3. Be present and prepared - there are fewer cues from others to rely on, so you can't go off on your own and expect to hear an obvious signal as to when the music is changing. In many cases, you are the person others are cuing off of. As such, you need to know your parts really well and execute them precisely. You should be doing this anyway, but it's more important in this situation.
4. Embrace the melody. In my case, when the guitar solos, I can comp in a traditional sense, but I can also play a variation of the melody under the solo. This can be helpful to the soloist and others to help provide them with the cues they need (see point #3).
5. If appropriate, you can add in a little slap and pop, but only if it truly fits the song. As another poster suggested, Larry Graham invented this technique because he didn't have a drummer; therefore, it definitely can work, especially on songs that already have slapping. However, it is generally not a good idea to add slapping into songs that don't already feature it, unless you can slap as well as Larry can.
6. Dial you tone into the mix and the room, not what you usually do when practicing alone. This should be something you do anyway (actual tone vs. bedroom tone), but it's even more important when playing without a drummer. You can't be rattling the room and churning out mud when others are depending on you to keep time.
7. Use an 8 string or 12 string sparingly. One other option you may be tempted to use would be an 8 or 12 string bass (the ones with the octave courses). I have tried this a few times with mixed results. On the one hand, using a bass like this makes me simplify my playing, and it fills in some of the sonic space in a smaller group setting. On the other hand, the octave courses usually require a little more drive/distortion to sound good, and they tend to be more audible than the bass strings. As such, they are not always good for helping others keep time. YMMV, but I've found these types of basses better with a drummer and one guitarist situations.
Hope this helps.
