I say the loan is unnecessary. It causes the very risk that would put them out of business. They do not need that much starting capital to begin doing this and a guild house to store the ore is not cost effective. You do not want to store the ore for a long time anyway, a quick turnover is the safest and most profitable way to do business. Paying a couple million trias for a house to store ore is not a good way to go. Guards would probably work best to start out and then they'd have enough trias in about a month to expand from there, if successful of course.
If they did do the loan, working on some quick numbers, best case, it'd take 10,640 ores (0 slags, full 188 trias profit with their own smelter) to make 2 million trias. If they could buy an average of 500 ores a day, it'd take ~22 days to pay back the loan. That doesn't seem impossible to me. Since it sounds like they don't have their own smelter, it'd take ~44 days if they split the 188 down the middle with the smelter, slags won't be too much of a problem, 1-3% delay, 5-15 ores a day. I'd check with Trasok and Gardr, maybe they'd share some information on how many platinum ingots they buy per day, I'm sure it must be well over 500. If it is closer to 2,000, then 500 should be possible to compensate for the loyal miners and miners that can smelt their own.
So is it legal? I'd say so, why not? They have just as much right to buy ore and offer an angle compared to any other smelter out there. I don't really see the difference between them offering 1100 per ore and some other smelter. And smelters are outbidding Gardr now anyway, so they are just another buyer entering the market.
Will it create conflicts? Absolutely, a bunch of them, and that may be why it won't work unless the stronger smelters and guilds are okay with it. If the loan is done, it'll be easy for competition to put their loan in default by offering free smelting, so diplomacy and cooperation will be a must.
As a smelter, I wouldn't mind them being around. I don't think there is enough work for probably 90% of the smelters out there however since it would take about an hour to smelt a full days worth of ore, but if I happened to be around and was offered 100 trias per ore to smelt 500 platinum ores, I think making a quick 50k wouldn't be such a bad thing. It'd be interesting to see if that is how it would work or if it would just turn into a chaotic mess of a market. The pure miners would definitely win out on this one, though.