If the walking foot/even feed foot is made for zig-zag machines, you can use zig-zag stitches - but if you use a stitch which alternates forward and backward feed, the foot won't coordinate with the machine's feed and the stitch may not look right.
When you have uneven stitches with your zig-zag, do you have skipped stitches? Or is the length between the stitches uneven? Or is the width of the zig-zag uneven?
If it's unevenness in the length, try using the even feed foot and/or applying a little more pressure with the pressure adjustment, so that the feed dogs are controlling the fabric better. If you can't do that, try loosening the thread tension a tiny bit at a time and see if that helps. Check the backside of the stitching after every adjustment - at some point, the tension is going to get too loose and you'll have loops of needle thread on the back and you'll know to put some tension back on the needle thread.
If it's unevenness in the width of the stitch, the mechanism that moves the needlebar from side to side might need oiling (especially on a vintage machine) or (if you have a selector dial or toggle to select the stitch width) it could be that the width selector isn't fully seated and might need to be oiled.
If it's a computerized machine, I haven't a clue about those at all. I have to go to the manual almost every time I use one of those and I'm always afraid I'll break something.
This is one of the things I love about my "old gals," if I do manage to break something, I can usually figure out what it is and fix it pretty quickly. :)