Yes.
From the IRC. (underlining is mine)
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SECTION P2608
- - MATERIALS EVALUATION AND LISTING
- - - P2608.1 Identification.
Each length of pipe and each pipe fitting, trap, fixture, material and device used in a plumbing system shall bear the identification of the manufacturer.
- - - - P2608.2 Installation of materials.
All materials used shall be installed in strict accordance with the standards under which the materials are accepted and approved. In the absence of such installation procedures, the manufacturer’s installation instructions shall be followed. Where the requirements of referenced standards or manufacturer’s installation instructions do not conform to the minimum provisions of this code, the provisions of this code shall apply.
All manufacturer's installation instructions I have seen state that the drain pan drain is to be drain to a floor drain or to the outdoors.
- P2801.2 Installation.
Water heaters shall be installed in accordance with this chapter and Chapters 20 and 24.
- SECTION M2005
- - WATER HEATERS
- - - M2005.1 General.
Water heaters shall be installed in accordance with the manufacturer’s installation instructions and the requirements of this code. Water heaters installed in an attic shall conform to the requirements of Section M1305.1.3. Gas-fired water heaters shall conform to the requirements in Chapter 24. Domestic electric water heaters shall conform to UL 174 or UL 1453. Commercial electric water heaters shall conform to UL 1453. Oiled-fired water heaters shall conform to UL 732.
- SECTION G2408 (305)
- - INSTALLATION
- - - G2408.1 (305.1) General.
Equipment and appliances shall be installed as required by the terms of their approval, in accordance with the conditions of listing, the manufacturer’s instructions and this code. Manufacturers’ installation instructions shall be available on the job site at the time of inspection. Where a code provision is less restrictive than the conditions of the listing of the equipment or appliance or the manufacturer’s installation instructions, the conditions of the listing and the manufacturer’s installation instructions shall apply.
- - - Unlisted appliances approved in accordance with Section 2404.3 shall be limited to uses recommended by the manufacturer and shall be installed in accordance with the manufacturer’s instructions, the provisions of this code and the requirements determined by the code official.
Now we go back to the Plumbing part of the IRC.
- P2801.5 Required pan.
Where water heaters or hot water storage tanks are installed in locations where leakage of the tanks or connections will cause damage, the tank or water heater shall be installed in a galvanized steel pan having a minimum thickness of 24 gage (0.016 inch) (0.4 mm) or other pans for such use. Listed pans shall comply with CSA LC3.
- - P2801.5.1 Pan size and drain.
The pan shall be not less than 11/2 inches (38 mm) deep and shall be of sufficient size and shape to receive all dripping or condensate from the tank or water heater. The pan shall be drained by an indirect waste pipe having a minimum diameter of 3/4 inch (19 mm). Piping for safety pan drains shall be of those materials listed
in Table P2904.5.
- - P2801.5.2 Pan drain termination.
The pan drain shall extend full-size and terminate over a suitably located indirect waste receptor or shall extend to the exterior of the building and terminate not less than 6 inches (152 mm) and not more than 24 inches (610 mm) above the adjacent ground surface.
I suspect those references should do the trick. 