Are you sure you are creating the master track? You need to go to Master mode in order to play the Mixdown track. Tascam use the same term 'Master' to refer to both Mix and Master files - no wonder I get confused
If you stay in Mixdown mode having mixed, pressing play just plays the tracks pre-mix, i.e. it allows you try mixing again by pressing record. Only when you switch to Master mode does it start playing back the mix'd file. If you added reverb during the mixdown phase, it should appear here. I've just double-checked with my DP32SD and it definitely works with both reverb & guitar delay effects.
When you're in Master mode, you can press record to overwrite that mix'd 'master' file with the final mastering effects using the EQ & Comp functions. You don't have to perform this step if you're happy with the mix'd file.
VTRACK & MASTER TRACK were references to the Mixer Block Diagram in the user manual. If you're not too phased by the diagram, you can trace through the audio flow and see how the insert & send effects work - can be instructive or mind-boggling depending on your level of nerdiness
Just to clarify adding reverb when mixing, set In & Out times then go to Mixdown mode. Go to the Mixer screen and check Send Master-1 level is turned up, then for all tracks to be reverb'd, turn their respective Send Eff-1 on, and the levels up. Go to the Effect screen and configure Reverb as reqd. Press Record. Move faders as reqd. You should hear the reverb as it mixes the tracks to create the master file. I guess if you can hear reverb at this point then you're doing everything right so far.
When you switch to Master mode, press Play and you should hear the master file with reverb. The track faders no longer work as you are listening to the master file.