DMX uses 0-255 for each of 512 addresses, not 0-128. However, if you use the DMXSimple library with an arduino that has an Atmega168 it will only output the first 128 channels (due to RAM constraints), but you are likely to have an Atmega328 (if you purchased your board any time recently) which supports all 512 channels. You are also not required to transmit all 512 channels.
I have made DMX receiving devices using a SN75176 (same as a MAX485). I haven't interfaced mine to a tablet, but if I were going to do it I would get an Ethernet shield and plug it into my wifi network. Sounds a lot easier than messing with bluetooth, especially since my range would be better.