As long as you hit cr.hp meaty, you can combo into U1. They are mostly really situational though and the damage for a raw U1 is usually better. For instance, you can do EX TK cannonstrike on Oni into cr.hp xx U1. This works because Oni gets pushed backwards so far and kinda falls into your cr.hp. Giving you enough frame advantage to link it.
Another example is when you block a spiral arrow from cammy, you can punish with cr.hp xx U1 (because it hits meaty again), but raw U1 just does more damage as a punish (and is way easier to hit).
Another example is on Abel’s roll (because he’s invincible throughout the roll, and punishable at the end, the cr.hp hits meaty):
Another example is hitting cl.mp or cl.hp on counterhit + crouching opponents and then cr.hp, on some characters they go backwards so far with their head that they just fall into your cr.hp, making it hit on the last active frames. Which gives you enough frame advantage to link it into u1:
(see description on who this works on).
This one actually has some use, as you can combo into U1 after you hit a frame trap.
There are way more situations. Like hitting a jump-in attack or EX divekick on Akuma and then you do cr.hp. It only works if you space it perfectly. And it’s so situational that I decided not to do a video about it. Also, doing a jump-in attack or EX divekick and going directly into U1 (without the cr.hp) does more damage too. It’s cool, but you’re giving up guaranteed damage for style points. Which is just stupid, if you ask me.
The important thing is hitting the cr.hp meaty enough.
One final thing to add, is that you can also combo into U1 on trades. Cr.hp, cl.mp and cl.hp can all be combo’d into U1 on trade. But you have to be really ready in order to get the ultra out in time. With cr.hp it’s do-able because if you get a trade or counter-hit, you could already buffer the Ultra motion just in case you hit them. But cl.hp/cl.mp rarely trades and you usually just get a counter-hit (and counter-hits don’t combo into U1 with cl.mp/cl.hp). So it’s probably not worth it to buffer the ultra motion all the time for these ones.