There was definitely a period where Datadog seemed to be talking up OTel but not actually doing anything of note to support that ecosystem.
I'd say in the last year or two, they've done a bit of a 180 and been embracing it quite a lot.
One major change is that they not only added support for the W3C Context header format but actually set it as the default over their own proprietary format.
The reason that's a pretty big deal is that W3C Context is set as a MUST for OTel clients to implement so it goes a long way to making interoperability (and migration) pretty painless.
Prior to that, you could use OTel but the actual distributed aspect (spans between services linking up) probably wouldn't work as OTel services wouldn't recognise the Datadog header format and vice versa.
There are, of course, still some features that you would miss out on by using OTel over the Datadog SDKs like I don't believe the profiler would work necessarily but that's a tradeoff to be made.