Pobjoy has never 'sprayed' with his PA25 (235) but the machine is a great Banner & glider tower. In fact the 'pull up' for a banner launch is not needed for spraying other than to avoid obstacles around fields. Glider launching is airframe friendly but the engine requires careful use on the descent to avoid shock cooling, and of course both operations are not carrying a hopper load which means you are well below max weight.
The top struts/fittings on a Pawnee are very important and subject to some fairly strict inspections but the basic wing is a lift junkie not an aerobatic tool. If you happen to be pulling some G and dump at the same time it is probably going to increase the G very quickly and 'possibly' the wings outboard of the struts will be taking the extra strain. A stripped out PA 25 without the spray equipment is an express lift and of course has no large fuel load, so the elevator input should be careful.