I have heard there can be issues when dissimilar metals are in prolonged contact. Would that apply to titanium and chromoly? Ive got may eye on a new titanium fork for my old chromoly frame bike.
As the comments to the question reasonably state, the problem of dissimilar metals contacting is really not applicable in the case of a fork and a headtube, because there is no direct contact.
The fork contacts either bearings' balls or one of bearings' races. Balls rotate, so unless you leave your bicycle in a cellar for a year, they will not get a chance of chemically reacting to the point they stick. And if the race binds, so what, the bearing will still rotate, and if the case of bearings replacement procedure the fork still can be extracted and races removed.
There should be enough of consistent grease to prevent both bearings' rusting and materials binding. That is the thing that one can control when installing a new fork, and then periodically refresh it with a new grease.
Where things may bind is where heterogeneous surfaces contact and do not move relatively to each other. The most notorious pair is seatpost and seattube. For a titanium fork, the stem/steering tube contact point should be something to watch for instead.