Yes, a 30" undermount single bowl kitchen sink with a garbage disposal can typically fit in a 34" sink base cabinet. The sink base cabinet size is typically larger than the actual sink size to provide enough space for installation and proper fitting. A 34" sink base cabinet should have sufficient room to accommodate the 30" sink and allow for any required adjustments during installation.
However, it's essential to ensure that the sink base cabinet has the necessary depth and height to accommodate both the sink and the garbage disposal comfortably. Also, consider the plumbing connections and clearance requirements for the garbage disposal.
Before making a purchase, measure the interior dimensions of the sink base cabinet to confirm that it can accommodate the sink and garbage disposal properly. Additionally, consult the product specifications and installation guidelines provided by the sink and garbage disposal manufacturer to ensure a proper fit and installation. If you have any doubts or concerns, it's best to consult with a professional plumber or installer for expert advice.