I'm a little confused by your post. You thought he had an abscess and the vet thinks that it's lamitis because of the tenderness in the toe, and because the hoof is trimmed CONCAVE? And the swollen legs are due to tendonitis. That's how I interpreted it.
First....is the tender toe/frog only in one foot or two?
Tendon issues...cold hosing and a liniment with a leg wrap and bute sound like good advice.
The laminitis/abscess question. First...if the hoof is CONCAVE, the there's not a problem with the trim. Concave is ideal. If it's suddenly gone FLAT, or has a bulge, that could indicate a crappy trim at best or even founder rotation. But before the bone rotates, usually the horse will have that telltale stance leaning waaaay back on his hinds, and normally it would affect both fronts, not just one, though it certainly is possible to affect only one foot.
Abscesses can mimic laminits in a couple of ways. First...the hoof can be so touchy, the don't want to put any weight on it, and there can be a bounding digital pulse and heat in the affected hoof. However, most abscesses only occur in one foot (or both if they are results of a previous founder episode). It can come on suddenly( with no feed change). Can be a result from any hoof trauma, a stone bruise, nail puncture, etc. and is the hoof's way of cleaning up the damage. It's just so painful because the hoof is rigid enough there's no room for extra fluid, so just before it pops like a giant pimple, it becomes very ouchy..just like a pimple on your face can hurt (and your skin is much more elastic and you don't even stand on your face LOL). Once the abscess pops, the pain is relieved immediately.
If your horse is abscessing, or foundering, soft footing will make him more comfortable. However, I would treat them slightly different.
Abscesses can be helped along with an espsom salt soak to draw out the pus. Your vet, if he deals with the hoof A LOT, could cut it to drain (though I don't recommend, because cutting before it's ready to pop doesn't let the blood vessels seal off the pus pocket and introducing foreign material can make the infection septic (go into the blood and spread)). A lot of vets don't mess with hooves as much, and while are capable of diagnosing a lot things, farriers DO tend to spot hoof issues more readily, as they are more focused on the foot, the vet has to know the whole body. So you might rather have a trimmer/farrier do the hoof work. Abscesses can occur anywhere in the foot.
If it's founder, being stall bound is the last thing you want. If it were my horse, I'd turn him out to exercise himself, trust me, if he's hurting, he won't be moving more than he can. Cut back his grain a little while he's out of commission (don't want to add to his problems) and keep his feet rasped every couple of weeks so the hoof can "reattatch" as it grows out. If you let it go 6-8weeks, the weak spot created by his laminitis episode will be easily made worse from mechanical leverage created by hoof growth. Once he's past the acute stage of pain, handwalking on firm, even surfaces will help speed that growth and healing. Lamitits is painful because the white line is detatching from the top (the wall is separating from coffin bone at the hairline where the inflammation is) and frequently the pain is actually from that "unzipping" of the connective white line. The sole isn't what's sore so much, until later, after the bone has rotated and is pressing through the sole material. If it's founder, an aggressive trim removing the wall at the toe to sole level will actually make him more comfortable, because the weight is now on the sole instead of the white line.
I would have another vet that specializes in hooves , or a well respected experienced trimmer/farrier take a look. Sounds more like an abscess at the moment to me.