BGR Controller voiced concern regarding the procedures used by another controller working arrivals to BHB; the reporter alleging facility training regarding this subject is needed.

Narrative

An SF340A was inbound to BHB. The ILS system is OTS for replacement; and the SF340A was unable to perform a RNAV approach. Aircraft was being vectored for approach. Topic of cruise clearance and possible use were being discussed. I was making IDS entries and heard the Developmental terminate RADAR service with the SF340A and frequency change aircraft. At that time; the SF340A was 2;800 FT north of BHB. Approximately 6 minutes later a Citation X was being vectored for visual approach and assigned 3;000 FT. The aircraft requested the visual approach but the SF340A had not yet canceled. The Citation X was vectored over BHB at 3;000 FT while efforts to contact the SF340A via telephone were being initiated by Supervisor. If the SF340A was issued a cruise clearance; it would appear that the last assigned altitude; 3;000 FT; is the altitude that needs to be protected. If aircraft was on a visual approach; it would seem imprudent to vector the Citation X over airport at the SF340A last assigned altitude. RADAR coverage at BHB is poor below 2;500 due to RADAR antenna being located at BGR with a small ridge of hills between the RADAR and BHB. BHB is basically a Non-RADAR operation for IFR operations. Recommendation; a reiteration of the correct procedures to be used with multiple arrivals on visual approaches or cruise clearances at BHB. When the SF340A was not assigned an altitude below 3;000; is that altitude available to subsequent arrivals over the airport prior to the SF340A canceling IFR?