I want to use Houdini for Procedural terrain generation, so that everytime the player loads in, the level is different. Is it possible for this functionality to exist at Runtime?

As far as I know, that is not currently supported by Houdini Engine. The current workflow is to generate things at editor time, bake them to standard Unreal assets and then use that in a regular way.
It would be possible to generate many variations, bake those out and then in Unreal randomly pick one of those at the start of each level. The result would a good number of variations, which you could potentially better screen for issues and the result would be a more carefully crafted experience.

In Unreal randomizing between multiple heavy assets comes with its own gotchas, depending on how you do it.
For example if you have a blueprint that selects from a list of landscapes, make sure that the references are all soft and you only load the landscape that you actually use.

thanks for explaining