yes and no. it all depends on their personalities!!
for example the wierd mixes iv had:
- pseudocrenilabrus nicholsi (dwarf, maxes at 4in) and red zebra (bigger, maxes at 6in)
- juvie red zebra and auratus (1.5 in each) and oscars (5in at time)
- buffalo head cichlid (dwarf, maxes at 4in) and red/OB/cobalt zebras (bigger, maxes at 6in)
- dwarf flag cichlid (dwarf, maxes at 3in) and oscar (bigger, usual at 12in) = i have these two happily mixed together right now (flags 1in oscars 5 & 6in)
iv also had two short-finned Bettas attempt to spawn while living in an mbuna tank.
seriously if u have nice personalitied fish u can do anything :L u just have to find the sweet ones in a bunch then put the dwarves in, but provide plenty of protection.
i dont recommend mixing countries. that can go very wrong. but keep the fish fairly similar or know what u r doing with the fish and ur ok.
what fish were u looking at? xxxx