What is an alternative in Feijoada to smoked ham or beef?
If you want to remove the meat completely, many "meat replacements" like tempeh and tofu are available in smoked varieties.  Most of these simply have liquid smoke AKA "Natural Smoke Flavoring" added as part of their process, but actual smoked varieties do exist.

Smoky flavors can also be attained from the following


Freshly roasted cumin 
Spanish style smoked paprika
Chipotle or other smoked chiles
Liquid Smoke
Some porters, stouts, and especially rauchbiers
Lapsang Souchong tea
Smoked salt
Katsuobushi/Bonito flakes (also adds a distinct fish flavor)