can I tell the cops I am happy with those people being on my land?
You're assuming that a police officer will accept your formulation of the question as being about whether you are "happy" or not about the presence of the protesters.
The most likely structure of the interaction is that your easement-holder will ring the police to say that a trespass is occuring which interferes with his rightful use of the land (via the easement).
The protesters may be asked whose permission they have to be present. They will either indicate that they have none, or they may say they have permission from you.
The question will then be put to you: are these visitors present with your permission, or are they indeed trespassers? Or, if they came onto the land without explicit permission, do you ratify their occupation of the land by granting them permission now, or are they present without your permission now?
If you grant permission, then you may become liable to your neighbour for frustrating the use of the easement. And if you do not grant permission, then the police may well remove the protest.
Beneath that it seems the easement holder could have them removed as trespassers interfering with the easement.
Doesn't any duty you might have to support the holder defending the easement depend on the details of your contract?
Similarly, whether 200 people are allowed on your land is a different thing from whether they're allowed near the easement, and again from what they might do there.
You need to ask a lawyer qualified to act in your particular jurisdiction.
– Robbie Goodwin Sep 15 '23 at 19:22