If I didn't have a lot of money, and I was saving it to spend on someone who brought me joy, I think it would make me feel good. I enjoy spending money on other people more than I enjoy spending it on myself. That is one thing that always makes me very happy, even when money is tight. So if I saved up and got someone a gift, and then they sat me down and told me they are concerned about my spending habits and making assumptions about my money... I honestly might be a bit offended or hurt, y'know?
Even when people don't have a lot of money, it's still okay for them to splurge on treats every once in a while. Some people like buying a cup of fancy coffee. Others might go out to eat. Others, grab a movie. This person might save up to be splurging on something that brings him happiness, and it probably makes him feel good to do it. I can totally empathize with someone finding more joy in spreading love and support through money, than using that money to buy himself occasional treats. Perhaps that is what he is doing - and having his gift rejected probably would feel like a bummer.
You said that this person has never mentioned money issues before, and that's where the problem lies, in my opinion. Unless this person has explicitly spoken to you about their money issues, it might be construed as rude to tell them how they should spend their money. Unless they have made their finances your business... Then confronting them and asking them not to spend money kind of crosses the line between what is your business and what is their business. They are a grown adult. They aren't a child who cannot be trusted to make responsible financial decisions. They aren't a submissive who has asked to give up control of their finances. Their decisions are their decisions, and it is their responsibility and their choice on what to spend it on.
If they are spending LOADS of money and it clearly makes you uncomfortable, then you should block them. Anyone who makes you uncomfortable isn't worth keeping around. That's a good rule of thumb to follow for any camming circumstance. Or, if this person flat out tells you that money is super tight, or explains in detail about their finances. Then, they are making it your business, y'know? Which kinda gives you permission to voice any concerns you might have. But, I personally would feel pretty miffed if someone made assumptions about my finances and told me that I wasn't spending my money wisely, when I was just spending money on things that brought me happiness. That would feel a bit patronizing to me, y'know? Because that means they thought they knew better than me about my own money and how I should spend it.
Obviously, you have a sweet heart, and you aren't meaning it as patronizing at all. You are coming from a kind and loving place, and want the best for your members, and that is admirable. And you might be right that money is tight for them. But it still might bring them joy to share a little of what they have in support of the people who bring them happiness. Adults are capable of making their own decisions. You aren't responsible for what other people spend their money on. You are responsible for your finances, your career, your business, and taking care of yourself and your family. You can't make yourself responsible for every member who comes into your life, cuz that can lead to emotional burn out faaaast.
Edit to add: This is just my opinion, however. The fact that it is causing you concern or distress is valid. The good thing about this business is that we can decide our own morals, and we don't have to compromise them for anyone. If this continues to upset you, then by all means, do what you have to do in order to feel better about your job. You decide what makes you feel good, and where you stand on any issue! You are not a bad person for taking the money that is offered, ESPECIALLY when they have not brought up any financial woes. You are not taking advantage of them and you don't need to feel guilty. You are just recognizing that they are adult enough to make their own decisions. But ultimately, you know yourself best! If this is going to continue to make you feel bad, then it's not worth it.