Shamefully n00b question ahead.

If I wanted to make a program that ran on a NES (hardware or emulator), does it matter which assembler to use? Would all of them, knowing which format I need to write the NES rom in, be able to produce the same thing?

I suspect the answer is yes, but being unfamiliar with 6502 assembly programming tools I don't want to pick one and find out it doesn't do what I want.

NES emulators use a special file format that supports bank switched ROM images. A standard 6502 assembler won't generate the right format file, you'll need one that understands how to build the header at the start of the file.

There is some information on NEW tools here http://nesdev.parodius.com/

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Andrew Jacobs
6502 & PIC Stuff - http://www.obelisk.me.uk/
Cross-Platform 6502/65C02/65816 Macro Assembler - http://www.obelisk.me.uk/dev65/
Open Source Projects - https://github.com/andrew-jacobs

I've had a lot of success using asm6 for NES programming, and it lends itself well to other 6502 platforms as well.

I'm using MADS, and until now, it was able to generate binary file compatible with any platform was needed.

You just need to know the format structure.

Specialized assembler would safe you a little (really a little) work.