Can I use a reused can for serving food

Food canned in steel cans (commonly called "tin cans" though none are made from tin), is generally considered safe - obviously we buy a lot of it at the store, and dedicated home canners can actually use steel cans themselves, with the cost of a special lid sealer device. Home canning with lined steel cans is considered safe by the FDA and USDA, at temperatures between 212F and 250F (pressure canning).

Modern cans are lined with an epoxy or other polymer lining that protects the can from corrosion, thus limiting the chance of contamination or spoilage. This liner usually contains small amounts of BPA (the chemical blamed for some potential long-term health problems), but amounts in different cans varies wildly, and the amount of BPA that is considered hazardous is also up for debate. If it matters greatly to you, you can get "BPA-free" canned food from some retailers (though some tests have found BPA even in "BPA-free" cans). Caveat emptor.

I would say that using cans to serve food would be safe, given a few caveats, mostly related to the liner:

• Make sure the cans liner hasn't been damaged with scratches by sharp tools. Tin plating is a bit toxic and food contaminated by tin shouldn't be consumed, but it usually takes a long time for even very acidic food to break down the tin through a scratch in the coating. Even if there was a scratch I think it would be impossible for enough tin to get into the food to exceed the very high safety limits of 200mg/kg. Easy to avoid the problem entirely by scooping the food out of the old can with something plastic or silicon.
• Don't heat the can above the temperature of boiling water. The liners are good up to around 240F at least, because that is roughly the temperature things are pressure sterilized at. If you are just serving out of the can rather than cooking in the can you should be fine.
• Sharp edges - The opened can has sharp edges, make sure that you press the sharp edges down so they aren't likely to catch someone's finger or tongue (if the food is good enough that they are licking the cans clean!).
• I won't get into the whole BPA thing deeply here - society in general seems comfortable with the small amount of BPA in most can liners, and I don't think you'd be "negligent" to use regular cans. If you feel strongly about it, use BPA-free cans from some brands sold at Sunflower Market, Whole Foods, Trader Joes or other "natural living" retailers.

The idea sounds cool, and I bet people will enjoy it! I'd recommend removing the cat-food labels, though. ;)

If all you're doing is taking clean dry recycled cans, and filling them with food for immediate consumption I can't see there's any food safety problem at all. The can contents would have been commercially sterile when purchased and the tin plate and laquer are reasonably robust - any undamaged surfaces must be suitable for food contact. Watch out for sharp edges, tho'.

Food grade cans are usually made from thin steel with a very thin tin coating. The top and bottom lid seams also contain a "plastic" material to ensure an airtight seal

Cans for storing acidic foods should have a very thin plastic layer on the inside only

As cans are pressure boiled to sterilise them, they should take the heat of a dishwasher OK

I wouldn't scrub the insides though, as you may partially flake off the plastic layer if it has one

You should be able to put acidic food in non-plastic-coated cans if it is only for serving purposes and not for storage purposes

If you are willing to settle for the 'effect' of serving food from cat food cans I would suggest you consider removing the labels from Tuna cans, as they are similar in size. During an episode of Good Eats Alton Brown recommends Tuna cans as rings for cooking English muffins. If they are good enough to cook with they should do fine for serving. (I don't think I need to tell you to clean them first...)

You should also consider using a "Safe Edge Can Opener" like this one available on Amazon. Traditional can openers or pull tops can leave an unsafe edge which you probably want to avoid.