It would be better than a wooden table, but the best welding top surface is steel or a cast iron grid (acorn table).
The stainless will reflect most of the arc and you won't be able to securely tack items to the table if you are into that kind of thing. Lots of guys tack tabs and ledges to the table top to help fixture their work.
If it's what you have and it fits your scope of work, there's nothing wrong with it. If it's in good condition, it won't be for long though. That's something to consider. You might be able to trade or sell it for a larger steel topped table. Not that you have to - a stainless top will work fine.
Stainless works great especially for aluminum. I use mine for TIG welding. You may put some burn marks in it but otherwise its great. I've been using mine for years.
Stainless has a great propensity to twist, warp, buckle and otherwise move in just about every direction possible when subjected to heat. You would need a fairly extensive gridwork of stiffeners welded to the underside I would think, in order to maintain a fairly true, flat surface.
I don't know what kind of welding you're going to be doing. If you are going use it for MIG or arc welding, it might not be the best thing. Besides being very reflective and subject to warpage, spatter sticks extremely well to stainless. Thick mild steel or cast iron tops seem to work best.