At the moment they appear somewhat of an obstacle to full takeover of Thailand by western backed liberals, at least judging from how much propaganda and political agitation is coming from the NGO ecosystem in Thailand against the monarchy.
But as we all know monarchies are fickle and opportunist, and if the West courts or bribes them enough the US may well get all they want anyway from Thailand, monarchy or no. So short term they are at best a stumbling block for the imperialists.
Long term it's up to the Thai people to decide what should happen to the monarchy. We don't get a say. But as a communist i firmly believe that monarchies belong in the dustbin of history.