I don't have much experience with this breed myself (not that I know of anyway!). I know some breeds are simply better suited to eventing than others but I don't tend to go by breed.
I think whats more important is whether he will be fit and sound enough, whether he is a confident jumper etc etc. You see where I am going with this? I try not to focus on the breed, more on the individual.
I don't have any experience with them, but just about anything can event lower levels. My mare is a Welsh/Appendix/Belgian and she does great up to novice. I think it's just on a horse to horse basis and depends how far you want to go with it.
Where are you? Some countries have more "riding type" standardbreds than others. Here in Aus, we have a LOT of harness type standies and very few that are really good riding types - but a LOT of them can really jump! Depends on the level you want to do I guess, standies make GREAT lower level allrounders and with the right training can make really nice jumpers and eventers. You just want to make sure the dressage isn't getting too much for them because dressage is REALLY important now and a good dressage score is often the difference between first and outside of the placings! I find that VERY few standardbreds have a good enough canter to do really well in dressage but if you find one that does, and that isn't ridiculously long in the back (harness conformation, a long back is considered to be a good thing in a racing standy), I think you'll find you have a nice eventer.
A huge upside to the standardbred, at least in Australia, is that most of them have the most beautiful nature! My old horse was a standie and he put up with so much from me, you wouldn't believe. I'd have another one - for a pleasure horse or low-level allrounder/eventer - in a heartbeat.
Just don't jump before your horse is 4 at the very youngest and definitely no higher than 18 inches until it's 5. Jumping's really hard on growing bones and if you jump them real young their long-term soundness can be affected.
I live in Ohio so most of the standardbreds aren't completely fullblooded (alot of quarter horse and thoroughbred lines) from the Amish and all the stock sales. I got him from a lady and she got him from the a stock sale but not sure. I don't think he's full blooded because of his shorter back and he has a canter more like a sport horse, but yes were only training in dressage right now.
Sounds nice, got pics? From your description he could do well, although you don't want his back TOO short because a really short back inhibits bascule over jumps and therefore limits scope. It's all a balancing act, especially with an eventer.
Edit; but MY eventer is REALLY long-backed and he did pretty well in his younger days because he loves it so much - passion overcomes a lot!
I don't think he has a short back but shorter than most standardbreds I've ridden and of course he's not full blooded he has some paint and thoroughbred I believe but I think he definitely has standardbred in him, that's what most people are telling me at least