I'm sorry to hear that your fellow chewed up an aluminum can and I understand your concern that he may have swallowed some pieces.
I don't that him chewing up the can is related to him having pneumonia, except it sounds he has recovered enough and feels well enough to be mischievous.
I do not recommend inducing vomiting in cases where dogs may have eaten sharp objects like metal shards. The chances of tearing their esophagus or stomach as it contracts to force the sharp pieces out is much too high.
In this case we need to try and hope that we can get any possible shards to pass through his gastrointestinal tract safely.
To help I recommend starting with feeding him a Vaseline (or any generic petroleum jelly) sandwich. Take a slice of whole wheat bread, slather with vaseline as you would peanut butter on a slice of bread, cover with a second slice. Feed it to him bite sized piece by piece or he will make a huge vaseline mess. This adds fiber and hopefully makes the pieces slip rather than catch.
For the next few days, until the shards pass, he'll need to be fed a bland diet with lots of fiber added in small meals several times a day, 4 to 6 meals is ideal. We do this so the pieces are surrounded, the gut isn't irritated by contracting on just sharp metal.
You can feed a homemade bland, higher fiber diet. You can make a homemade diet mix with 1/3 boiled, lean hamburger or boiled, white, skinless chicken, all fats drained off of the meat, and 2/3 boiled, plain white rice. Add 2-4 tablespoons of canned pumpkin, (not pie filling, just pumpkin), to each meal for fiber.
You'll need to check his stools frequently for pieces in the next few days.
Signs that things aren't going well, and he needs an immediate veterinary visit, are vomiting, a tense painful belly, lack of an appetite, a fever (more than 103.5F rectally), frank blood or black tarry stools, and lethargy.
If you aren't seeing fragments in the next day or two a veterinary visit and an abdominal radiograph to see where the shards are is an option. Most metal will show up on radiographs, though not all. If in doubt at all that things aren't going well it is always best to have him checked.
Once the pieces are passed and he's feeling well then start mixing in his regular food, adding a little more regular and less bland at each meal. It should take a week to get him converted back to regular food.
The pieces should pass within the next 3-5 days.
Let me know if you have any questions.