If you ever watch a video of Southern Pride or other commercial smokers with the rotating food trays, all of the food is "basting" the other food with drippings. That's a feature of the smoker design.
About the only issue I could see would be if you had been running food below on a fixed grate (or in the rotating racks) that was mostly done, and you add raw chicken above. Might sear off in a few seconds like Dave said, but I would not be comfortable mixing raw with done like that.
Howdy..... Dave didn't say that.... Chef JimmyJ noted that it was OK.....
Personally, I would never place chicken above beef or pork.... Chicken needs to cook to 165 and beef and pork to 145... NOW, it may sear off and kill the chicken pathogens but I wouldn't take the chance.... that's me.... Sometimes I eat beef that's been cooked to an internal temp of 130...
There is a pasteurization table that allows for "Safe to Eat" foods cooked to a lower temperature as long as TIME is involved.... the added time, at lower temps, will kill pathogens of interest...
Below are some TIME and TEMPERATURE charts for those interested.....
FSIS Guidance on Safe Cooking of Non-Intact Meat Chops, Roasts, and Steaks April 2009
Temp °F / Time for 5.0 log Reduction
Unit Time
130.......... .86 min.
131 ...........69 min.
132.......... 55 min.
133.......... 44 min.
134............ 35 min.
135............. 28 min.
136 ..............22 min.
137 ...............18 min.
138 ...............14 min.
139............... 11 min.
140 ..............9 min.
141.............. 7 min.
142 .............6 min.
143 .............5 min.
144 .............4 min.
145 .............3 min.
146 ..............130 sec.
147.............. 103 sec.
148 ..............82 sec.
149 ..............65 sec.
150............... 52 sec.
151................ 41 sec.
152................ 33 sec.
153 ................26 sec.
154 ................21 sec.
155 ................17 sec.
156 .................14 sec.
157 ..................11 sec.
158 ...................0 sec.
159 ....................0 sec.
160 ....................0 sec.
The required lethalities are achieved instantly when the internal temperature of a cooked meat product reaches 158 °F or above. Humidity must be considered when using this Time/Temperature table.
This Time/Temperature table is based on Thermal Death Curve for Salmonella in Beef Emulsions in tubes (Derived from Goodfellow & Brown1, 1978) Regulatory Curve obtained from Jerry Carosella, Deputy Director, Microbiology Division, Science and Technology. All times that were a fraction of a minute or second was rounded up to the next whole number (e.g., 16.2 seconds for 155 °F was round up to 17 seconds).
________________________ 1. Goodfellow, S. J. and W. L. Brown. 1978. Fate of Salmonella Inoculated into Beef for Cooking. Journal of Food Protection. 41:598-605.
POULTRY CHART...
Temperature........
...................... Time
°F (°C).............. 12% fat
136 (57.8)......... 81.4 min
137 (58.3)........ 65.5 min
138 (58.9)........ 52.9 min
139 (59.4)........ 43 min
140 (60.0)........ 35 min
141 (60.6)........ 28.7 min
142 (61.1)........ 23.7 min
143 (61.7)........ 19.8 min
144 (62.2)........ 16.6 min
145 (62.8)........ 13.8 min
146 (63.3)........ 11.5 min
148 (64.4)........ 7.7 min
150 (65.6)........ 4.9 min
152 (66.7)........ 2.8 min
154 (67.8)........ 1.6 min
156 (68.9)........ 1 min
158 (70.0)........ 40.9 sec
160 (71.1)........ 26.9 sec
162 (72.2)........ 17.7 sec
164 (73.3)........ 11.7 sec
166 (74.4)........ 0 sec
Table C.2: Pasteurization times for a 7D reduction in Salmonella for chicken and turkey (FSIS, 2005).