I’m not sure if you consider the risk being that of a scammer trying to obtain BTC using the need to aid Ukraine as a pretext, or whether you consider that those BTCs donated could be more prone to be under less control of their proper usage, than through traditional fiat donations.

Be it as it be, cross-referencing the information here and there should mitigate the risk of sending of BTCs (et al) to a rogue address. In addition, yet not on its own, choosing well-known organizations should help reduce the chances of sending to a scammer. Even if there may be some sort of risk involved of ending-up sending some finds to some scummy scammer somewhere, despite being extra cautious, the need to aid the Ukrainians should prevail (be it in crypto, fiat, logistics, supplies, whatever).