I think you will be OK, although someone who was currently employed at an airline might have a competitive edge on recent flight time.

If you can afford it and have the time, I would go ahead and do the ATP...

- It will make you more competitive.
- Airlines will probably provide it on the training ride, but some might not. It takes a higher level of instructor qualification to do an ATP ride as opposed to an SIC 121 PC. There may not be enough DPEs to go around.
- You can conduct re-training during a type ride or a PC. You cannot do that on an ATP ride. If you already have the ATP, that would give you more margin for error on the new-hire checkride.
- When jumpseating, mainline guys won't make snide comments about your lowly commercial ticket.